DE102011005420A1 - Memory device for storing electrical energy, has monitoring device with controllable grounding electrode for diverting charging current of memory cell based on mass of monitored physical quantity of memory cell - Google Patents

Abstract

A memory device (101) has rechargeable memory cell (103) which is charged by using electric current. A monitoring device (105) monitors a physical parameter of the memory cell. The monitoring device is comprised of controllable grounding electrode (107) for diverting the charging current of memory cell based on mass of the monitored physical quantity. The grounding electrode is comprised of shift element (209) for providing electrical short circuit between memory cell and charging circuit. An independent claim is included for method for operating memory device.

Description

The invention relates to a storage device for storing electrical energy. The invention further relates to a method for operating a storage device for storing electrical energy.

State of the art

Lithium ion battery packs must not be overcharged to prevent damage. In order to prevent overcharging, there are various protective measures in the charger to interrupt a current flow. However, if these protective measures are not sufficient, the current flow in the battery pack itself must be interrupted. However, this requires expensive and complex switching elements. In addition, these switching elements always have a resistance in the closed state, so that efficiency during charging or discharging is impaired.

Disclosure of the invention

The object underlying the invention can therefore be seen to provide a storage device for storing electrical energy, wherein an overcharge is prevented, without an efficiency during charging or discharging is impaired.

The object underlying the invention can also be seen in providing a corresponding method for operating a memory device for storing electrical energy.

These objects are achieved by means of the subject matter of the independent claims. Advantageous embodiments are the subject of each dependent subclaims.

In one aspect, a storage device for storing electrical energy is provided. The storage device is preferably formed as a rechargeable battery. Such a battery can also be referred to as a battery pack. For example, the rechargeable battery may be in the form of a lead-acid battery, a lithium-ion rechargeable battery, a lithium-polymer rechargeable battery, a lithium-iron-phosphate rechargeable battery, a lithium titanate rechargeable battery, a lithium-sulfur rechargeable battery, a sodium-nickel rechargeable battery. Chloride accumulator, a sodium-sulfur accumulator, a nickel-iron accumulator, a nickel-cadmium accumulator, a nickel-metal hydride accumulator, a nickel-hydrogen accumulator, a nickel-zinc accumulator or as a tin-accumulator Sulfur lithium accumulator may be formed.

The memory device comprises a memory cell which can be charged by means of an electrical charging current. The memory cell is preferably a galvanic cell. In the context of accumulators, such a galvanic cell may also be referred to as a secondary cell. Furthermore, the memory device has a monitoring device which can monitor a physical quantity in the memory cell. The physical variable is preferably a temperature in the memory cell and / or an electrical voltage in the memory cell. Such a temperature may also be referred to as a storage cell temperature. Such a voltage may also be referred to as a memory cell voltage.

The memory device further comprises a ground conductor, which is controllable by means of the monitoring device. The ground arrester is formed so that it can derive the charging current to ground depending on the monitored physical quantity.

According to another aspect, there is provided a method of operating a memory device for storing electrical energy, wherein the memory device comprises a memory cell. In a first step, the memory cell is charged by means of an electrical charging current, wherein a physical quantity in the memory cell is monitored. Depending on the monitored size, the electrical charging current is dissipated to ground.

The invention thus includes the idea that, depending on the monitored physical size of the memory cell, the electrical charging current is discharged to ground during a charging process. Since the charging current is derived to ground, the memory cell can not be charged further in this respect. Thus, an overload of the memory cell is effectively avoided in an advantageous manner. Furthermore, even a defective charger, which can not automatically turn off a charging current automatically, does not lead to an overcharge of the memory cell, since an interruption of the charging process is carried out in the storage device itself, ie independent of a charger.

Preferably, the electrical charging current is dissipated to ground when the electric storage cell voltage is above a predetermined voltage value. Preferably, the electrical charging current is dissipated to ground when the memory cell temperature is above a predetermined temperature value.

In another embodiment, a plurality of memory cells are formed. In order to increase a voltage provided by the memory cells, the memory cells can be connected in particular in series or connected in parallel to increase a total capacitance of the memory cells. Preferably, it can also be provided that some memory cells are connected in parallel and some memory cells are connected in series, wherein the memory cells connected in parallel to the series-connected memory cells are in turn connected in parallel or in series. In particular, it is sufficient for a plurality of memory cells that a physical quantity in a memory cell is above a predetermined value in order to stop the charging process and to derive the electrical charging current to ground.

In another embodiment, the ground conductor comprises a switching element for electrically shorting a charging circuit connected to the memory cell. To such a charging circuit, an electric charger is connected in particular for charging the memory cell. Such a charging circuit comprises, for example, one or more contacts for contacting or connecting the electric charger. As a result, that is, that the charging circuit is short-circuited, no charging current flows to the memory cell, so that they can not be overloaded in an advantageous manner.

Preferably, the switching element is a transistor, in particular a field effect transistor (FET), a relay or a controllable short-circuit element.

In particular, the switching element is connected in parallel to the charging circuit.

In particular, a switching element in the sense of the present invention has two switching states: an open switching state in which the charging circuit is not short-circuited, so that an electrical charging current for charging the memory cell can flow and is not dissipated to ground, and a closed switching state, in which Charging circuit is short-circuited, so that no electric charging current for charging the memory cell can flow into the memory cell, but is derived to ground. When the switching element is in the open switching state, the switching element may also be referred to as an open switching element. When the switching element is in the closed switching state, the switching element may also be referred to as a closed switching element.

According to a further embodiment, the switching element is a reversible switching element. Reversible here means in particular that the switching element between the open switching state and the closed switching state can be switched back and forth. Thus, advantageously, the memory cell can be further charged or recharged when the physical size again corresponds to a permissible value, since the reversible switching element can be opened again, so that the electric charging current is not further derived to ground, but for Charging the memory cell to this flows.

During charging of the memory cell, the switching element is open, so that no electric current can flow through the switching element. The electric charging current thus flows to the memory cell in order to charge it. Only when the monitored physical variable is above a certain value, the switching element is closed by means of the monitoring device, so that a short circuit is formed in the charging circuit. The charging current now no longer flows to the memory cell, but is derived to ground. In this case, in particular, a charging voltage provided by means of the charging device is connected to ground via the switching element such that at least the maximum possible charging current is dissipated.

In another embodiment, a discharge circuit is formed, which is connected to the memory cell, so that over this the memory cell can be discharged. Preferably, the charging circuit and the discharge circuit are formed separately. But it can also be provided that the charging circuit is equal to the discharge circuit. The memory device thus has a common charge / discharge circuit.

The invention will be explained below with reference to preferred embodiments with reference to figures. Show here

1 a storage device for storing electrical energy,

2 another storage device for storing electrical energy,

3 a flowchart of a method for operating a storage device for storing electrical energy and

4 another storage device for storing electrical energy.

1 shows a storage device 101 for storing electrical energy. The storage device 101 includes a memory cell 103 and a monitoring device 105 which is a physical quantity in the memory cell 103 supervised. The physical variable is preferably a memory cell temperature and / or a memory cell voltage. In an embodiment, not shown, a plurality of memory cells may be provided, which are connected in parallel and / or in series. Depending on the monitored physical quantity, the monitoring device controls 105 a ground conductor 107 , which can derive an electrical charging current to ground.

2 shows another storage device 201 for storing electrical energy. The storage device 201 includes two memory cells 203a and 203b , wherein respective physical quantities in the memory cells 203a and 203b by means of a monitoring device 205 be monitored. Furthermore, a ground arrester 207 for deriving an electrical charging current to ground. The ground conductor 207 is by means of the monitoring device 205 controllable, wherein the control is performed depending on the monitored physical quantity. The ground conductor 207 includes a switching element 209 thus formed, one with the memory cells 203a and 203b electrically connected charging circuit (not shown). In the switching element 209 it is preferably a transistor, in particular a field effect transistor, a relay or a controllable short-circuit element.

3 shows a flowchart of a method for operating a memory device for storing electrical energy. In a first step 301 For example, a memory cell of the memory device is charged by means of an electric charging current. During the charging process, a physical quantity in the memory cell is monitored. Depending on the monitored size will be in one step 303 the electrical charging current derived to ground. Thus, advantageously, overcharging of the memory cell can be effectively avoided if a physical size of the memory cell, for example a temperature or a voltage, is above a critical value.

4 shows another storage device 401 for storing electrical energy. The storage device 401 includes several memory cells 403 , which are electrically connected in series. It may also be provided in an embodiment, not shown, that the memory cells 403 are connected in parallel. In another embodiment, not shown, at least some of the memory cells 403 in series and the other memory cells connected in parallel. The memory cells 403 can be charged by means of an electric charging current.

Furthermore, the storage device comprises 401 a monitoring device 405 which each have a physical size in the memory cells 403 supervised. Preferably, the monitoring device monitors 405 a memory cell voltage and / or a memory cell temperature. The monitoring device 405 controls a switching element depending on the monitored physical quantities 407 which is parallel to the memory cells 403 is switched. The switching element 407 is in this respect parallel to a charging circuit 409 comprising two charging contacts 409a and 409b connected. In the switching element 407 it is preferably a transistor, in particular a field effect transistor, a relay or a controllable short-circuit element.

With the charging circuit 409 is by means of the two charging contacts 409a and 409b a charger 411 connected, so the charger 411 the memory cells 403 can charge by means of an electric charging current.

As long as the physical quantities in the memory cells 403 are below a predetermined value, the switching element 407 open, ie there is no current through the switching element 407 flow. The entire electric charging current flows to the memory cells 403 to charge these. The charging circuit 407 is not shorted so far.

But once in one of the memory cells 403 the physical quantity exceeds the predetermined value, the charging process is to be aborted. In general, the charger should 411 to do this automatically. But should the voltage in this memory cell or the storage device 401 continue to increase, it is assumed that the charger 411 can not end the charging, for example because it is defective or because it has no automatic shutdown. In this case, then in particular the switching element 407 closed, leaving the charging circuit 409 shorted. In particular, this is a means of the charger 411 Provided charging voltage via the switching element 407 connected to ground in such a way that at least the maximum possible charging current is derived.

Since this circuit is used only in case of failure, is a discharge of the storage device 401 advantageously not critical.

In an embodiment not shown, the monitoring device comprises 405 a microcontroller, which has a total voltage of the memory cells 403 monitored via an analogue / digital (A / D) channel. In another embodiment, not shown, the memory cell voltages can be digitally output directly to the microcontroller. This applies analogously to the temperature.

In a further embodiment not shown, the memory cell voltages and / or the memory cell temperatures can also be monitored analogously by means of a monitoring module, which in the event of an error, in particular in the event of an overload, either sends a signal to a microcontroller which switches the controllable short circuit, that is to say the switching element. or directly drives the controllable short circuit.

The invention offers the particular advantage that neither in a charging circuit nor in a discharge circuit added an additional resistance by an additional switching element, so that efficiency in normal operation, ie in particular when the charging circuit is not short-circuited and the storage device is charged or discharged, not is impaired. In particular, no change to the charging contacts or discharge contacts is required, so that the memory device remains fully backward compatible and still meets current standards. Furthermore, in the design of the protection circuit, only a maximum charging current and not a significantly higher discharge current must be considered.

In summary, the invention provides a way to prevent overcharging a memory cell of a memory device due to a defective charger. Compatibility with old battery packs is not compromised in an advantageous manner.

Claims (6)

Storage device ( 101 ) for storing electrical energy, with a rechargeable by means of an electrical charging current memory cell ( 103 ) and a monitoring device ( 105 ) for monitoring a physical quantity in the memory cell ( 103 ), characterized in that a means of the monitoring device ( 105 ) controllable ground arrester ( 107 ) for deriving the charging current to ground depending on the monitored physical quantity. A memory device according to claim 1, wherein the ground conductor ( 107 ) a switching element ( 209 ) for electrically shorting one with the memory cell ( 103 ) connected charging circuit ( 409 ). Memory device according to claim 2, wherein the switching element ( 209 ) is a transistor, a field effect transistor, a relay or a controllable short-circuit element. Memory device according to claim 2 or 3, wherein the switching element ( 209 ) parallel to the charging circuit ( 409 ) is switched. Method for operating a storage device ( 101 ) for storing electrical energy with a memory cell ( 103 ), wherein the memory cell ( 103 ) is charged by means of an electric charging current and a physical quantity in the memory cell ( 103 ) are monitored, characterized in that the electrical charging current is derived depending on the monitored size to ground. The method of claim 5, wherein deriving the electrical charging current includes shorting a capacitor to the memory cell. 103 ) connected charging circuit ( 409 ).

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