METHOD FOR PREPARING AN EMERGENCY ENERGY STORE FOR OPERATION

Abstract

Described and shown is a process for preparing an emergency energy storage device, with at least one energy storage element for operation, whereby the emergency energy store is designed to provide emergency electrical energy for at least one energy consumer, whereby the energy (E.sub.L) which can be drawn from the emergency energy storage and/or the peak output (P.sub.max) which can be drawn from the emergency energy storage is determined and the operational readiness is established as soon as the energy (E.sub.L) which can be drawn from the emergency energy storage and/or the peak output (P.sub.max) which can be drawn from the emergency energy storage has reached a definable minimum energy value. A process for preparing an emergency energy storage device for operation in which the emergency energy storage is discharged via a discharging device and the heat occurring at the internal resistance (R.sub.i) is used to heat the emergency energy storage device.

Claims

1. A method for preparing for operation an emergency energy storage unit having at least one energy storage element, wherein the emergency energy storage unit is designed to provide emergency electrical energy for at least one energy consumer, wherein the energy E.sub.L withdrawable from the emergency energy storage unit and/or the peak output P.sub.max withdrawable from the emergency energy storage unit is determined and the operational readiness is established as soon as the energy E.sub.L withdrawable from the emergency energy storage unit has reached a definable minimum energy value and/or the peak output P.sub.max withdrawable from the emergency energy storage unit has reached a definable minimum output value, characterized in that if the determination has the result that the energy E.sub.L withdrawable from the emergency energy storage unit does not reach a definable minimum energy value and/or the peak output P.sub.max withdrawable from the emergency energy storage unit does not reach a definable minimum output value, the emergency energy storage unit is then discharged via a discharging device in order to use the heat generated during the discharging of the emergency energy storage unit at its internal resistance R.sub.i to heat the emergency energy storage unit.

2. The method for preparing an emergency energy storage unit for operation according to claim 1, characterized in that the energy E.sub.L withdrawable from the emergency energy storage unit and/or the peak output P.sub.max withdrawable from the emergency energy storage unit is determined again after discharging the emergency energy storage unit to heat the emergency energy storage unit, and that the emergency energy storage unit is recharged if the redetermination of the energy E.sub.L withdrawable from the emergency energy storage unit and/or the peak output P.sub.max withdrawable from the emergency energy storage unit had the result that the energy E.sub.L withdrawable from the emergency energy storage unit did not reach a definable minimum energy value and/or that the peak output P.sub.max withdrawable from the emergency energy storage unit did not reach a definable minimum output value.

3. The method for preparing an emergency energy storage unit for operation according to claim 1, characterized in that the discharging process of the emergency energy storage unit takes place for a specified period of time or that the period of time is redetermined in individual cases for each discharging process.

4. The method for preparing an emergency energy storage unit for operation according to claim 1, characterized in that the determination of the energy E.sub.L withdrawable from the emergency energy storage unit and/or of the peak output P.sub.max withdrawable from the emergency energy storage unit is determined continuously during the discharging.

5. The method for preparing an emergency energy storage unit for operation according to claim 1, characterized in that before discharging of the emergency energy storage unit, the emergency energy storage unit is charged by an amount such that after the discharging of the emergency energy storage unit to heat the emergency energy storage unit, the energy E.sub.L withdrawable from the emergency energy storage unit and/or the peak output P.sub.max withdrawable from the emergency energy storage unit is sufficient for determining the operational readiness.

6. The method for preparing an emergency energy storage unit for operation according to claim 1, characterized in that the discharging device comprises the one energy consumer or at least one of the energy consumers.

7. The method for preparing an emergency energy storage unit for operation according to claim 1, characterized in that the discharging current takes place by means of a pulse width modulation, wherein, in particular, the peak discharging current is limited to the maximum permissible pulse current of the current circuit comprising the emergency energy storage unit and the discharging device.

8. The method for preparing an emergency energy storage unit for operation according to claim 1, characterized in that at least one physical variable that allows for a statement to be made regarding the core temperature of the one energy storage element or of the several energy storage elements of the emergency energy storage unit is measured, the core temperature is calculated based on the physical variable or the physical variables, and the discharging of the emergency energy storage unit takes place at least until the core temperature has reached a definable temperature threshold.

9. The method for preparing an emergency energy storage unit for operation according to claim 8, characterized in that aging effects of the emergency energy storage unit, which aging effects change the relationship between the physical variable or the physical variables and the core temperature, are taken into consideration in the calculation of the core temperature.

10. The method for preparing an emergency energy storage unit for operation according to claim 8, characterized in that the physical variable or the physical variables include the capacitance C of the emergency energy storage unit and/or the internal resistance R.sub.i of the emergency energy storage unit.

11. The method for preparing an emergency energy storage unit for operation according to claim 1, characterized in that the energy storage elements comprise capacitors, in particular ultra-capacitors.

12. A method for preparing a pitch system for a wind turbine system for operation, wherein the pitch system has at least one emergency energy storage unit having at least one energy storage element, characterized in that a method according to claim 1 is applied to the one emergency energy storage unit or to at least one of the emergency energy storage units of the pitch system.

13. A computer program product with program instructions for executing a method according to claim 1.

14. A pitch system for a wind turbine system, wherein the pitch system comprises at least one emergency energy storage unit with at least one energy storage element, characterized in that the pitch system is designed for executing the method according to claim 12.

15. A wind turbine system with a pitch system according to claim 14.

Description

[0043] In detail, there are then a multitude of options for designing and further developing the process according to the invention for preparing an emergency energy storage device for operation. To that end, reference is made to the claims dependent on claim 1, as well as to the subsequently detailed description of preferred exemplary embodiments of the invention with reference to the drawing.

[0044] The drawing shows the following:

[0045] FIG. 1 schematically shows the connection between the temperature T of an energy storage element and its internal resistance R.sub.i,

[0046] FIG. 2 shows a flowchart of a preferred embodiment of the process according to the invention; and

[0047] FIG. 3 schematically shows a part of a pitch system according to the invention.

[0048] FIG. 1 schematically shows the connection between the temperature T of an energy storage element and its internal resistance R.sub.i. To this end, the temperature T has been applied to the y-axis and the internal resistance R.sub.i of an exemplary energy storage device has been applied to the x-axis and the diagram of FIG. 1. It is clearly shown that when the temperature T drops below a certain value, the internal resistance R, increases greatly. The temperature T from which the internal resistance R.sub.i greatly increases depends on the type of energy storage device. For ultra-capacitors, this temperature T is frequently in the range of 0; depending on the type however, the internal resistance under certain circumstances is sufficient even starting at −15° C., for enabling reliable emergency operation. The temperature, thus, depends on the properties of the selected emergency energy storage and the other dimensioning of the pitch drive and should; therefore, be individually selected for any type.

[0049] FIG. 2 shows a flowchart of a preferred embodiment of the process according to the invention. After the start (S) of the process, first to the emergency energy storage is charged (L) in order to ensure that sufficient energy is stored for the subsequent process steps in the emergency energy storage. Said process step can particularly be omitted when it can be assumed that sufficient energy has already been stored for the subsequent process steps in the emergency energy storage device, for example, from a previous start, and the system is placed back into operation after just a brief interruption, for example after maintenance work.

[0050] In the next step, the energy E.sub.L drawable from the emergency energy storage and/or the peak output P.sub.max drawable from the emergency energy storage is determined (B). The determination of the peak output P.sub.max drawable from the emergency energy storage can preferably be carried out by methods that do not require a total discharge of the emergency energy storage. For capacitors used as an emergency energy storage, contrary to chemical emergency energy storage devices, such as lead-acid batteries, there is a direct relationship between the voltage difference at the start and at the end of a partial discharging process and the drawn output such that the stored residual energy can be reliably deduced merely from a discharging time or charging time of a few seconds. As the emergency energy storage was only loaded for a few seconds with the discharging current, there may be sufficient residual energy still present to not require a renewed charging upon a measurement via the discharging process and beyond. Preferably, the capacitance determination; however takes place by means of a charging process so that energy is supplied to the emergency energy storage instead of drawn from the emergency energy storage.

[0051] If the determination (B) of the energy E.sub.L drawn from the emergency energy storage and/or the peak output P.sub.max drawable from the emergency energy storage is the result of the energy E.sub.L drawable from the emergency energy storage achieving a definable minimum energy value and/or the peak output P.sub.max drawable from the emergency energy storage achieving a definable minimum energy value, then the operational readiness is determined (X) and, particularly, a signal is generated to the prioritized control device, whereby the signal indicates the operational readiness.

[0052] If the determination (B) results in the energy E.sub.L drawable from the emergency energy storage not achieving a definable minimum energy value and/or the peak output P.sub.max drawable from the emergency energy storage not achieving a definable minimum output value, then first the emergency energy storage device is discharged via a discharging device in order to heat up the emergency energy storage by means of its internal resistance R.sub.i (E). Following this, the energy E.sub.L drawable from the emergency energy storage device and/or the peak output P.sub.max drawable from the emergency energy storage is determined (B) again. This procedure heats the emergency energy storage device regardless of whether the emergency energy storage has a low temperature or not. This procedure can always be applied when the parameters of the emergency energy storage reliably indicates that the emergency energy storage device cannot overheat due to a one-time discharge. This is always the case when the load resistance is high enough in order to limit the discharging current such that an overheating of the emergency energy storage is excluded. If, for example, the so-called braking chopper is selected as the discharging resistor, then the breaking chopper is not only itself naturally configured to this load but prevents, with a resistance of typically 10 ohm, as is customary for a motor of 7 kW, an overloading of the emergency energies storage, without additional measures being required.

[0053] Alternatively, before a decision as to whether the emergency energy storage should first be discharged for heating the emergency energy store (1) by means of its internal resistance R.sub.i, or should be started at the same time as the charging without previous discharging, said decision can be made dependent on the temperature dropping below a measured temperature, for example the temperature within the housing in which the emergency energy storage (1) is housed and/or the internal resistance R.sub.i of the emergency energy storage device (1).

[0054] Typically, a converter is provided between a grid connection and the motors that provides, for example, an intermediate circuitry voltage of 420 V. In this case, the emergency energy storage is typically arranged on the inverter on the primary side, while the motors and, thus, the potential load resistors are connected to the inverter on the secondary side. Super-capacitors obtainable at the time of the application have, for example, an internal resistance of 0.08 ohm at a temperature of −40° C. With a pitch motor for an output of 7 kW, the resistance of the winding typically is 0.2 ohm. If the bank comprising super-capacitors with the winding of the pitch motor is loaded, a discharging current of approximately 150 A is set at the start of the discharging of the −40° C. cold emergency energy storage device, instead of the permissible 30 A set for the capacitors. The discharging current can the limited to an average of 30 A, based on a pulse width modulation starting at 20%, for example switch-on of the load resistor for a cycle period of the converter and a wait time of four cycle periods until the next switch-on, With a typical application, the switching frequency of the converter may be, for example, 8 kHz such that the winding of the pitch motor is switched on, for example, for 125 μs in an alternating manner and then disconnected from the emergency energy device for a time duration of 500 μs.

[0055] Based on a typical heating capacity of a super-capacitor cell of 60 Ws/K and a typical heating resistance of 11 K/W, the core temperature of the super-capacitors with a discharging current of 30 A can be raised by about 30 K, thus, to an operating temperature of −15° C., within 1000 seconds. With the capacitor type selected in this exemplary embodiments, the system can then be placed in operation at this temperature, as the cell has, to a great extent, achieved its original capacitance as well as a sufficiently low internal resistance.

[0056] Alternatively, the redetermination (B) can also continuously take place during the discharging (E) such that the two process steps essentially take place in parallel. If the redetermination (B) results in the energy E.sub.L drawn from the emergency energy storage achieving a definable minimum energy value and/or the peak output P.sub.max drawable from the emergency energy storage achieving a definable minimum energy value, then the operational readiness is determined (X) and, particularly, a signal is generated to the prioritized control device, whereby the signal indicates the operational readiness.

[0057] If the redetermination (B) results in energy E.sub.L drawable from the emergency energy storage not achieving a definable minimum energy value and/or the peak output P.sub.max drawable from the emergency energy storage not achieving a definable minimum output value, the emergency energy storage device is charged (L). The charging (L) may take place, for example, until the emergency energy storage is charged at 90%. Subsequently, the energy E.sub.L drawable from the emergency energy storage and/or the peak output P.sub.max drawable from the emergency energy storage is determined (B) again.

[0058] The loops formed by these steps L, B, E, and B will continue to run until one of the determinations (B) results in the energy E.sub.L drawable from the emergency energy storage achieving a definable minimum energy value and/or the peak output P.sub.max drawable from the emergency energy storage achieving a definable minimum output value. Alternatively, the loops can be interrupted after a defined maximum number of runs and an error signal is generated to the control device. Thus, when the emergency energy storage does not have the required minimum energy after 100 loop runs, for example, it can be concluded that the emergency energy storage has reached the end of its service life. With the error signal, a technician can be informed who must then replace the emergency energy storage before the system is placed back into operation.

[0059] If the process according to the invention is used, for example, in an application area in which only the energy E.sub.L drawable from the emergency energy storage is relevant and the peak output P.sub.max drawable from the emergency energy storage does not play any role, then only the energy E.sub.L drawable from the emergency energy storage is determined (B) and the operational readiness is determined (X), as soon as the energy E.sub.L drawable from the emergency energy storage has reached the specified minimum energy value.

[0060] FIG. 3 schematically shows a part of a pitch system according to the invention. The emergency energy storage device (1) has a plurality of energy storage elements (2), which are detailed by the circuit symbols of multiple capacitors in the figure. The emergency energy storage device (1) is connected to this in order to provide electrical emergency energy for an energy consumer (3). Furthermore, the emergency energy storage device (1) is still connected to a discharging device (4) and a charging device (5). The emergency energy storage (1) can be discharged for heating via the discharging device (4). The charging device (5) is used to charge the emergency energy storage device (1). Additionally, a control device (6) is provided, which is set up for processing program instructions for executing the process according to the invention. To this end, a computer program with corresponding program instructions can be stored in a data store of the control device (6). The control device (6) is connected to the remaining components for exchanging control signals via signal lines. For clarification purposes, the components are shown separately in FIG. 3. Within the scope of the invention, two or more components may also be combined into one assembly. A single component can also take on the tasks of multiple components. Thus, an electric motor can simultaneously form the energy consumer (3) the discharging device (4), and even the charging device (5) in the generator operation.

REFERENCE LIST

[0061] 1 Emergency energy storage [0062] 2 Energy storage element [0063] 3 Energy consumer [0064] 4 Discharging device [0065] 5 Charging device [0066] 6 Control device