Device and method for determining the capacitance of hybrid capacitive energy storage devices in a hybrid capacitive energy storage device, and switching station using a determination of capacitance of this kind

Abstract

The invention relates to an energy storage device (10) for an electromagnetic drive of a low-voltage switch, medium-voltage switch, or high-voltage switch, the energy storage device (10) comprising one or more capacitors (201, 202, 203) of a first capacitor type and one or more additional capacitors (301, 302, 303, 304, 305) of a second capacitor type, the first capacitor type including ceramic capacitors, film capacitors and / or electrolytic capacitors and the second capacitor type being a supercapacitor, and the at least one capacitor (201, 202, 203) of the first capacitor type and the at least one additional capacitor (301, 302, 303, 304, 305) of the second capacitor type being interconnected in parallel via an energy flow controller (100).

Description

[0001] Description

[0002] Device and method for determining the capacity of hybrid capacitor energy storage devices in a hybrid capacitor energy storage device and switchgear with such a capacity determination

[0003] The invention relates to a device and a method for determining the capacity of hybrid capacitor energy storage devices in a hybrid capacitor energy storage device and to a switchgear system with such a capacity determination device.

[0004] A hybrid energy storage device is an energy storage device that consists of at least two different energy storage types. A hybrid capacitor energy storage device is therefore an energy storage device that is formed with at least two different capacitor types. Such a hybrid capacitor energy storage device is useful when the electrical properties of the storage media exhibit significant differences in at least one parameter, for example, energy density and / or internal resistance.

[0005] In a hybrid capacitor energy storage system consisting of electrolytic capacitors and super capacitors, the basic electrical parameters differ as follows:

[0006] - An electrolytic capacitor has a low internal resistance with a relatively low capacitance and is therefore capable of high currents.

[0007] - A super capacitor has a high internal resistance and a high capacitance, which results in a high amount of available energy at moderate discharge currents.

[0008] Switching devices for low, medium or high voltage systems such as circuit breakers with electrical drives, for example magnetic drives, require a quantity of energy for a switching operation, which is usually stored in capacitors, since the auxiliary voltage supply of the switching device cannot provide the high power required for a switching operation, i.e. the amount of energy in a very short time.

[0009] Furthermore, in the event of an auxiliary voltage failure, i.e. a failure of the auxiliary voltage supply, the requirement must be met on a regular basis to ensure that a switching operation into the safe switching position OPEN, i.e. open or opened, is ensured for at least 5 minutes after the auxiliary voltage supply failure.

[0010] These two requirements result in the need to design the energy storage device in such a way that, on the one hand, a low electrical internal resistance for the switching energy and, on the other hand, a high storage capacity for the bridging time in the event of an auxiliary power supply failure is provided.

[0011] A hybrid capacitor energy storage system meets these requirements.

[0012] Furthermore, for long-term safe operation of a capacitor storage device, for example for a circuit breaker, cyclical capacitance measurement and monitoring of the capacitor storage device must be carried out in order to detect aging and spontaneous failures in a timely manner and to be able to react to them.

[0013] This also applies to hybrid capacitor energy storage systems. For capacitor energy storage systems, for example, the capacity of the entire capacitor energy storage system is determined. This is done by increasing the charging voltage slightly above the normal operating voltage and then discharging it in a controlled manner to the normal operating voltage, measuring current, voltage, and discharge times to determine the capacity. Such a capacity determination is not possible with a hybrid capacitor energy storage system, as a deterioration / reduction in the capacity of the electrolytic capacitors is not noticeable due to their low capacity compared to supercapacitors.

[0014] Electrolytic capacitors are known in the art as energy storage devices for electromagnetic drives, for example, for load and circuit breakers, particularly in medium-voltage switchgear. These are used because, when appropriately dimensioned, electrolytic capacitors can meet both requirements: low internal resistance for high short-term power for switching operation, as well as sufficient specific capacitance for the required bridging times in the event of an auxiliary power supply failure.

[0015] The object of the invention is to provide an alternative embodiment of the capacitance measurement on the hybrid capacitor energy storage device, which eliminates the disadvantages of the prior art.

[0016] The problem is solved by the independent claims 1 and 14 and the claims dependent thereon.

[0017] One embodiment relates to a capacity determination device for hybrid capacitor energy storage in a hybrid capacitor energy storage, wherein

[0018] • the hybrid capacitor energy storage device comprises one or more capacitors of a first capacitor type and one or more further capacitors of a second capacitor type,

[0019] • wherein the first capacitor type comprises ceramic, film and / or electrolytic capacitors and the second capacitor type is a supercapacitor, and wherein

[0020] • the at least one capacitor of the first capacitor type and the at least one further capacitor of the second capacitor type are connected in parallel to one another via a capacitance determination device, and wherein

[0021] • the capacity determination device o has an energy flow control, by means of which energy flow control the capacitors of the first capacitor type are optionally charged or the capacitors of the first capacitor type are charged together with the further capacitors of the second capacitor type, o has a control element which is arranged between the parallel-connected capacitors of the first capacitor type and the further capacitors of the second capacitor type in such a way that the discharge process of the capacitors of the second capacitor type takes place via the control element, a current flow from the capacitors of the first capacitor type to the further capacitors of the second capacitor type is prevented, and o has a capacity determination unit which determines a capacity from a charging current and the resulting voltage and preferred discharge time.

[0022] This arrangement makes it possible to avoid parallel operation of the first capacitor type and further capacitors of the second capacitor type via a conventional switching element, which leads to a reduction in installation space and costs.

[0023] The energy storage device, particularly for an electromagnetic drive for a vacuum interrupter in a low-, medium-, or high-voltage switchgear, is a hybrid energy storage device consisting of capacitors and supercapacitors. The capacitors are connected to the supercapacitors via an energy flow control system. The capacitors are designed for rapid energy delivery, i.e., high power delivery, to the electromagnetic drive to operate the drive, and the supercapacitors serve as energy storage devices if the auxiliary power supply of a switchgear fails.In the event of a failure of the auxiliary power supply, the supercapacitors are designed to take over the function of the auxiliary power supply and preferably to provide a sufficient operating voltage to charge the capacitors of the first type and thus to switch the switching device over a period of at least 5 minutes and thus to be able to carry out at least one opening operation.

[0024] The energy flow control is designed to regulate the energy flow between the capacitors of the first capacitor type and the further capacitors of a second capacitor type and preferably also the auxiliary voltage supply.

[0025] Due to the energy flow control, the charging time for the capacitors of the first capacitor type is reduced compared to the total charging time of the hybrid energy storage system, in particular since it is possible to initially charge only the capacitors of the first capacitor type and only then the capacitors of the second capacitor type.

[0026] Supercapacitors are also called electrochemical capacitors or ultracapacitors and are characterized by the fact that they do not usually have a dielectric in the conventional sense, but the energy is stored in double layers on the electrodes, with storage taking place both in the form of charge separation in the double layers and in the form of electrochemical storage.

[0027] In particular, a short charging time until operational readiness for switching operations is achieved by charging the capacitors of the first capacitor type first, followed by the charging of the capacitors of the second capacitor type. The bridging time in the event of an auxiliary voltage failure is therefore only achieved after the capacitors of the first capacitor type have been charged and after a short waiting period, which, however, is not detrimental to operational management. In addition, the use of supercapacitors ensures a longer bridging time in the event of an auxiliary voltage failure without increasing the charging times of the capacitors of the first capacitor type.

[0028] At the same time, a longer bridging time is achieved in the event of an auxiliary voltage failure, even with the same installation space.

[0029] It is preferred that the first capacitor type is an electrolytic capacitor.

[0030] It is also preferred that the first capacitor type has an energy density of at most 0.5 Wh / l and the second capacitor type has an energy density of at least 3 Wh / l, and / or that the second capacitor type has an energy density that is at least 5 times higher than that of the first capacitor type, and wherein the first capacitor type has a lower internal resistance than the second capacitor type.

[0031] It is further preferred that more than one capacitor of the first capacitor type are connected in parallel.

[0032] It is preferred that more than one capacitor of the second capacitor type are connected in series with each other.

[0033] In particular, it is preferred that the hybrid capacitor energy storage device further comprises a charge balancing circuit, wherein the charge balancing circuit is designed to transfer excess charges from supercapacitors with higher voltage to supercapacitors with lower voltage.

[0034] It is also preferred that the control element is a diode. The diode is arranged such that, on the one hand, the diode prevents a current flow from the capacitors of the first type to the further capacitors of the second type and, on the other hand, enables a current flow from the further capacitors of the second capacitor type to the capacitors of the first capacitor type.

[0035] It is also preferred that the energy flow control is provided by one or more bidirectional DC-DC converters.

[0036] In particular, it is preferred that at least one of the bidirectional DC-DC converters is designed to further perform the function of the control element.

[0037] It is also preferred that the energy flow control is formed with at least one unidirectional DC-DC converter for each flow direction.

[0038] In particular, it is preferred that at least one of the unidirectional DC-DC converters is designed to further perform the function of the control element.

[0039] A further embodiment relates to an electromagnetic drive for a vacuum interrupter of a low-, medium- or high-voltage switchgear, wherein the electromagnetic drive has a capacitance determination device for hybrid capacitor energy storage devices in a hybrid capacitor energy storage device according to one or more of the above embodiments.

[0040] Another embodiment relates to a low-, medium- or high-voltage switchgear, wherein the low-, medium- or high-voltage switchgear has an electromagnetic drive according to the preceding embodiment.

[0041] A further embodiment relates to a method for determining a capacitance in a hybrid capacitor energy storage device for a low-, medium- or high-voltage switchgear according to a previous embodiment, wherein to determine the capacitance of the hybrid capacitor energy storage device a) a first capacitance of the capacitors of the first capacitor type is determined by charging the capacitors of the first capacitor type to the voltage required for the capacitance measurement, wherein the further capacitors of the second capacitor type, the super capacitors, are not charged,so that the voltage of the additional capacitors of the second capacitor type is lower than the voltage of the capacitors of the first capacitor type, thus preventing a current flow from the additional capacitors of the second capacitor type to the capacitors of the first capacitor type, and thus the capacitance determination unit determines the capacitance of the capacitors of the first capacitor type; b) the total capacitance of the capacitors of the first capacitor type and the additional capacitors of the second capacitor type, i.e. of the entire hybrid capacitor energy storage device, is determined by the capacitance determination unit; and c) a further capacitance of the additional capacitors of the second capacitor type is calculated from the determined first capacitance and the determined total capacitance.

[0042] It is preferred that

[0043] - either step a) is carried out before step b) or step b) is carried out before step a), and

[0044] - step c) is carried out after steps a) and b).

[0045] With regard to the device according to the invention, all statements made above and below regarding the method according to the invention apply accordingly, and vice versa. In particular, the device according to the invention is designed to carry out the method according to the invention in any desired embodiment or a combination of desired embodiments. With regard to the advantages of the device according to the invention, reference is also made to the advantages described for the method according to the invention.

[0046] The invention is explained in more detail below using an exemplary embodiment. The specific embodiment of the exemplary embodiment is in no way intended to limit the general design of the method and device according to the invention; rather, individual design features of the exemplary embodiment can be freely combined with one another and with the features described above in any way.

[0047] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

[0048] The invention is explained in more detail below with reference to figures.

[0049] Figure 1: Schematic representation of a switchgear;

[0050] Figure 2: Exemplary equivalent circuit diagram of a hybrid capacitor energy storage device according to the invention;

[0051] Figure 3: Foot diagram for carrying out the procedure;

[0052] Figure 4: Example equivalent circuit diagram of a charge balancing circuit.

[0053] Figure 1 shows a schematic representation of a switchgear 1 with displays 4 and a user interface 6.

[0054] The displays 4 and the user interface 6 are analogue and / or digital.

[0055] Figure 2 shows an exemplary equivalent circuit diagram of a hybrid capacitor energy storage device 10 according to the invention. The hybrid capacitor energy storage device 10 has a capacity determination device 100 with an energy flow control, optionally with an energy supply, and a control element for connecting the hybrid capacitor energy storage device 10 to an electromagnetic drive and an auxiliary voltage source of a switchgear 1, wherein the energy flow control and the control element are further designed to regulate, i.e. control, the energy flow between the capacitors 201, 202, 203 of a first capacitor type and the further capacitors 301, 302, 303, 304, 305 of a second capacitor type.

[0056] Figure 2 also shows parallel-connected capacitors of a first capacitor type 201, 202, 203, here, for example, three electrolytic capacitors, which are designed to supply the electromagnetic drive with electrical energy for at least one switching operation. The capacitance-determining device 100 with the energy flow control and the control element is connected to the last electrolytic capacitor 203, and supercapacitors 301, 302, 303, 304, 305, here, for example, five supercapacitors, are connected in parallel via the capacitance-determining device 100. The supercapacitors are connected in series. A charge-balancing circuit 400 is optionally arranged in parallel with each capacitor.

[0057] Figure 3 shows a flow chart for implementing the method. In a first step 1000, the capacitance determination of the hybrid capacitor energy storage device 10 is initiated, and the capacitors 201, 202, 203 of the first capacitor type are charged to the voltage required for the capacitance measurement, for example, 3% to 5% above the predetermined operating voltage of the capacitors 201, 202, 203 of the first capacitor type, without charging the additional capacitors 301, 302, 303, 304, 305 of the second capacitor type, the supercapacitors. This is achieved by a control element, for example, a diode or a DC-DC converter.As a result, the voltage of the further capacitors 301, 302, 303, 304, 305 of the second capacitor type is lower than the voltage of the capacitors 201, 202, 203 of the first capacitor type and a current flow from the further capacitors 301, 302, 303, 304, 305 of the second capacitor type to the capacitors 201, 202, 203 of the first capacitor type is prevented and thus the following capacitance measurement on the capacitors 201, 202, 203 of the first capacitor type is not influenced by the further capacitors 301, 302, 303, 304, 305 of the second capacitor type.

[0058] In the second step 1100, the capacitance measurement is carried out on the entire system, whereby only the capacitors 201, 202, 203 of the first capacitor type contribute to the measurement.

[0059] In the third step 1200, the capacitors 201, 202, 203 of the first capacitor type are discharged again to the predetermined operating voltage.

[0060] In the fourth step 1300, the capacitors 201, 202, 203 of the first capacitor type and the further capacitors 301, 302, 303, 304, 305 of the second capacitor type are then charged to the voltage required for the capacitance measurement, for example again 3% to 5% above the predetermined operating voltage of the capacitors 201, 202, 203 of the first capacitor type and / or the further capacitors 301, 302, 303, 304, 305 of the second capacitor type.

[0061] In the fifth step 1400, the total capacitance measurement of the entire system is then carried out, with the capacitors 201, 202, 203 of the first capacitor type and the further capacitors 301, 302, 303, 304, 305 of the second capacitor type contributing to the measurement.

[0062] In the sixth step 1500, the capacitors 201, 202, 203 of the first capacitor type and the further capacitors 301, 302, 303, 304, 305 of the second capacitor type are discharged back to the predetermined operating voltage. In the seventh step, the capacitance of the further capacitors 301, 302, 303, 304, 305 of the second capacitor type is determined from the determined capacitance of the capacitors 201, 202, 203 of the first capacitor type and the determined total capacitance.

[0063] Figure 4 shows an exemplary equivalent circuit diagram of a charge balancing circuit 400 for, here, five supercapacitors 301, 302, 303, 304, 305.

[0064] The charge equalization circuit 400 has a voltage divider, here for example a resistor network with five resistors 410, 420, 430, 440, 450 as a voltage divider between a first potential 401, here for example a ground potential, and a second potential 402, here for example a positive voltage V +,. Furthermore, the charge balancing circuit 400 has, for example, four operational amplifiers 415, 425, 435, 445. The voltage difference between the first potential 401 and the second potential 402 corresponds to the theoretical charging voltage of the supercapacitors 301, 302, 303, 304, 305. However, since the actual capacitances of capacitors can deviate from the nominal capacitances, deviations in the range of ±5% to ±20% are possible, the charge equalization circuit 400 is constructed in such a way that the theoretical charge voltage is divided by means of the resistor network of resistors 410, 420, 430, 440, 450 as a voltage divider, and in the case of differing capacitances of the supercapacitors 301, 302, 303, 304, 305, the operational amplifiers 415, 425, 435, 445 act as voltage followers to achieve a voltage equalization corresponding to the respective capacitances of the respective supercapacitors. 301, 302, 303, 304, 305.For this purpose, the inverting input of each operational amplifier 415, 425, 435, 445 is directly connected to the output of the respective operational amplifier 415, 425, 435, 445. The operational amplifiers 415, 425, 435, 445 are each supplied with voltage by two cells, here supercapacitors 301, 302, 303, 304, 305.

[0065] The operational amplifier 445, referred to here as the lowest operational amplifier 445, is supplied with voltage through the ground contact 401 and the cell above it, i.e. at the output of the operational amplifier 435, here supercapacitor 302.

[0066] The operational amplifier 435 located above is supplied with voltage by the cell with the output of the operational amplifier 445, here supercapacitor 301, and the cell with the output of the operational amplifier 425, here supercapacitor 303.

[0067] The operational amplifier 425 is supplied with voltage by the cell with the output of the operational amplifier 435, here supercapacitor 302, and the cell with the output of the operational amplifier 415, here supercapacitor 304.

[0068] The top operational amplifier 415 is supplied with voltage by the cell with the output of the operational amplifier 425, here 303, and the cell with the input voltage 402, here supercapacitor 305.

[0069] If one or more supercapacitors 301, 302, 303, 304, 305 have a lower voltage than the desired capacitor voltage, the respective operational amplifier 415, 425, 435, 445 acts as a current source and charges the respective supercapacitor 301, 302, 303, 304, 305. The charge required for this is then taken from one of the neighboring supercapacitors 301, 302, 303, 304, 305.

[0070] If one or more supercapacitors 301, 302, 303, 304, 305 have a higher voltage than the desired capacitor voltage, the operational amplifier 415, 425, 435, 445 acts as a current sink and discharges the respective supercapacitor 301, 302, 303, 304, 305. The excess charge is then taken from one of the neighboring supercapacitors

[0071] 301, 302, 303, 304, 305. The charge balancing circuit 400 thus reduces voltages of supercapacitor 301, 302, 303, 304, 305 with too high voltage and thus increases voltages of supercapacitor 301,

[0072] 302, 303, 304, 305 with too low a voltage. This achieves charge equalization. In particular, such a charge equalization circuit 400 does not have any highly integrated, inductive or capacitive components, in particular no coils or other capacitors.

[0073] List of reference symbols

[0074] 1 switchgear;

[0075] 4 Display on switchgear 1;

[0076] 6 User interface of switchgear 1;

[0077] 10 energy storage units;

[0078] 100 Capacity determination device with an energy flow control and a control element;

[0079] 201 capacitor of a first capacitor type, e.g. electrolytic capacitor;

[0080] 202 Capacitor of a first capacitor type, e.g. electrolytic capacitor;

[0081] 203 Capacitor of a first capacitor type, e.g. electrolytic capacitor;

[0082] 301 capacitor of a second capacitor type, a supercapacitor;

[0083] 302 capacitor of a second capacitor type, a supercapacitor;

[0084] 303 Capacitor of a second capacitor type, a supercapacitor;

[0085] 304 Capacitor of a second capacitor type, a supercapacitor;

[0086] 305 Capacitor of a second capacitor type, a supercapacitor;

[0087] 400 charge balancing circuit

[0088] 401 first potential, for example earth potential;

[0089] 402 second potential, for example positive voltage V + ;

[0090] 410 resistance of the voltage divider;

[0091] 415 operational amplifiers;

[0092] 420 resistance of the voltage divider;

[0093] 425 operational amplifiers;

[0094] 430 resistance of the voltage divider;

[0095] 435 operational amplifiers;

[0096] 440 resistance of the voltage divider;

[0097] 445 operational amplifiers;

[0098] 450 resistance of the voltage divider.

Claims

Patent claims 1. Capacity determination device (100) for hybrid capacitor energy storage (10) in a hybrid capacitor energy storage (10), characterized in that - the hybrid capacitor energy storage device (10) comprises one or more capacitors (201, 202, 203) of a first capacitor type and one or more further capacitors (301, 302, 303, 304, 305) of a second capacitor type, - wherein the first capacitor type comprises ceramic, film and / or electrolytic capacitors and the second capacitor type is a supercapacitor, and wherein - the at least one capacitor (201, 202, 203) of the first capacitor type and the at least one further capacitor (301, 302, 303, 304, 305) of the second capacitor type are connected in parallel to one another via a capacitance determination device (100), and wherein - the capacity determination device (100) o has an energy flow control, by means of which energy flow control either the capacitors (201, 202, 203) of the first capacitor type are charged or the capacitors (201, 202, 203) of the first capacitor type are charged together with the further capacitors (301, 302, 303, 304, 305) of the second capacitor type, o has a control element which is arranged between the parallel-connected capacitors (201, 202, 203) of the first capacitor type and the further capacitors (301, 302, 303, 304, 305) of the second capacitor type in such a way that the discharge process of the capacitors (301, 302, 303, 304, 305) of the second capacitor type via the control element is carried out, a current flow from the capacitors (201, 202, 203) of the first capacitor type to the further capacitors (301, 302, 303, 304, 305) of the second capacitor type is prevented, and o has a capacitance determination unit which determines a capacitance from a charging current and the resulting voltage.

2. Capacitance determination device (100) according to claim 1, characterized in that the first capacitor type is an electrolytic capacitor.

3. Capacity determination device (100) according to one of the preceding claims, characterized in that the first capacitor type has an energy density of at most 0.5 Wh / l and the second capacitor type has an energy density of at least 3 Wh / l, and / or that the second capacitor type has an energy density which is at least 5 times higher than that of the first capacitor type, and wherein the first capacitor type has a lower internal resistance than the second capacitor type.

4. Capacitance determination device (100) according to one of the preceding claims, characterized in that more than one capacitor (201, 202, 203) of the first capacitor type are connected in parallel with one another.

5. Capacitance determination device (100) according to one of the preceding claims, characterized in that more than one capacitor (301, 302, 303, 304, 305) of the second capacitor type are connected in series with one another.

6. Capacity determination device (100) according to claim 5, characterized in that the energy storage device (10) further comprises a charge balancing circuit (400), wherein the charge balancing circuit (400) is designed to transfer excess charges from supercapacitors with higher voltage to supercapacitors with lower voltage.

7. Capacitance determination device (100) according to one of the preceding claims, characterized in that the control element is a diode.

8. Capacity determination device (100) according to one of the preceding claims, characterized in that the energy flow control is formed with one or more bidirectional DC-DC converters.

9. Capacity determination device (100) according to claim 8, characterized in that at least one of the bidirectional DC-DC converters is designed to further perform the function of the control element.

10. Capacity determination device (100) according to one of claims 1 to 7, characterized in that the energy flow control is formed with at least one unidirectional DC-DC converter for each flow direction.

11. Capacity determination device (100) according to claim 10, characterized in that at least one of the unidirectional DC-DC converters is designed to further perform the function of the control element.

12. Electromagnetic drive for a vacuum interrupter of a low-, medium- or high-voltage switchgear (1), characterized in that the electromagnetic drive has a capacity determination device (100) for hybrid capacitor energy storage (10) in a hybrid capacitor energy storage (10) according to one of the preceding claims.

13. Low, medium or high voltage switchgear (1), characterized in that the low, medium or high voltage switchgear (1) has an electromagnetic drive according to the preceding claim.

14. Method for determining a capacitance in a hybrid capacitor energy storage device (10) for a low-, medium- or high-voltage switchgear (1) according to claim 13, characterized in that for determining the capacitance of the hybrid capacitor energy storage device (10) a) a first capacitance of the capacitors (201, 202, 203) of the first capacitor type is determined by charging the capacitors (201, 202, 203) of the first capacitor type to the voltage required for the capacitance measurement, wherein the further capacitors (301, 302, 303, 304, 305) of the second capacitor type, the super capacitors, are not charged, so that the voltage of the further capacitors (301, 302, 303, 304, 305) of the second capacitor type is lower than the voltage of the capacitors (201, 202, 203) of the first capacitor type and thus a current flow from the further capacitors (301, 302, 303, 304, 305) of the second capacitor type to the capacitors (201, 202, 203) of the first capacitor type is prevented and thus the capacitance determination unit determines the capacitance of the capacitors (201, 202, 203) of the first capacitor type; b) the total capacitance of the capacitors (201, 202, 203) of the first capacitor type and the further capacitors (301, 302, 303, 304, 305) of the second capacitor type, i.e. of the entire hybrid capacitor energy store (10), is determined by the capacitance determination unit; and c) a further capacitance of the further capacitors (301, 302, 303, 304, 305) of the second capacitor type is calculated from the determined first capacitance and the determined total capacitance.

15. Method for operating a low-, medium- or high-voltage switchgear according to claim 14, characterized in that - either step a) is carried out before step b) or step b) is carried out before step a), and - step c) is carried out after steps a) and b).

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