Patent ID: 12249836

In these figures, identical elements use the same reference signs.

DETAILED DESCRIPTION OF THE INVENTION

The following achievements are examples. Although, the specification refers to one or several embodiments, it does not imply that each reference refers to the same embodiment or that the features apply only to a single embodiment. Simple features of different embodiments can also be combined to provide other embodiments.

The present invention refers to a method for managing a battery coupled to a power grid.

FIG.1represents a diagram of a power grid1and a plurality of sources3such as power plants, solar panels, wind turbines . . . coupled to this power grid1as well as a plurality of charges5such as houses, buildings or warehouses also coupled to the power grid. Batteries7are also coupled to the power grid and may act either as sources or as charges. The power grid1has a nominal frequency fn, for example 50 Hz but the actual frequency of the power grid1may vary around this nominal frequency fn. These variations are due to the differences that may occur between the power provided by the sources3and the power required by the charges5.

If the amplitude of these variations is higher than a predefined threshold or if they last longer than a predefined duration, these variations may lead to damages on the different equipments coupled to the power grid1.

Thus, different states of the power grid1have been defined:

A normal state wherein the absolute value of the gap with the nominal frequency is less than 200 mHz and the absolute value of the gap with the nominal frequency is not higher than 50 mHz for more than 15 minutes or not higher than 100 mHz for more than 5 minutes.

An alert state wherein the absolute value of the gap with the nominal frequency is less than 200 mHz and the absolute value of the gap with the nominal frequency is higher than 50 mHz for more than 15 minutes or higher than 100 mHz for more than 5 minutes. The normal state returns when the absolute value of the gap with the nominal frequency is less than 50 mHz.

An emergency state wherein the absolute value of the gap with the nominal frequency is more than or equal to 200 mHz. The normal state returns when the absolute value of the gap with the nominal frequency is less than 50 mHz.

In order to prevent damages on the batteries7, the present invention refers to the adaptation of at least one parameter for compensating frequency deviations around the nominal frequency fn occurring in the power grid1. This adaptation is achieved at predetermined time intervals, for example 15 minutes which is high enough to avoid introducing additional instabilities to the power grid1and to enable power grid management to oversee the behavior of the batteries7in the next few minutes. Other predetermined intervals, preferably higher than 15 minutes, for example 30 zo minutes may also be used. The management of the battery7is achieved in order to enable the battery7to provide or to absorb a power corresponding to a deviation of 200 mHz during 15 minutes.

The adaptation is achieved according to a state of charge SoC of the battery7and the amplitude of the frequency deviations during a predetermined duration.

FIG.2is a diagram of the distribution of the power in a battery7. The total power Pt of the battery7is divided into an active part Pa corresponding to the power engaged for power grid stabilization and a management part Pm reserved for the management of the state of charge SoC of the battery7. The distribution may correspond to approximately 80% of the total power Pt associated with the active part Pa and 20% with the management part Pm. For a battery having a total power of 25 MW, 20 MW may be associated with the active part and 5 MW may be associated with the management part. This ratio does not vary over time.

The power Pa engaged for power grid stabilization may be defined by the following equation:

Pa=K*(f−fn) with fn the nominal frequency, f the actual frequency and K the gain setting associated with the power Pa engaged for power grid stabilization.

Thus, the response by a battery7to a variation of the frequency of the power grid may be adapted by modifying the gain K or by modifying a setpoint Sp of the power Pm associated with the management of the state of charge SoC of the battery7. As indicated previously, the values of this gain K and this setpoint Sp are chosen according to the state of charge SoC of the battery7and the deviations of the power grid1frequency with respect to the nominal frequency fn. It has to be noted that the gain K and the setpoint Sp cannot be changed when the power grid1is in an alert state.

The management of these parameters may be represented by the flowchart ofFIG.3. The measured frequency f of the power grid1is compared to the nominal frequency fn and the gain K is applied to the difference f-fn to produce the power Pa engaged for power grid stabilization. The setpoint Sp is then added to the power Pa engaged for power grid stabilization to provide a battery power Pb which gives the state of charge SoC of the battery7. The state of charge SoC of the battery7is then transmitted to a management unit9which can provide a feedback loop toward the setpoint Sp and/or the gain setting K in order to adapt the values of the setpoint Sp and the gain setting K according to the state of charge SoC of the battery7. The adaptation of the values of the setpoint Sp and/or of the gain setting K is made at predetermined time intervals corresponding to intervals of at least 15 minutes, for example 30 minutes in order to prevent the introduction of an additional level of instability in the power grid1.

Different functioning modes associated with different states of charge SoC are defined as represented inFIG.4. The different modes, except the first mode1, comprise a high level band corresponding to a high state of charge SoC of the battery7and a low level band corresponding to a low state of charge SoC of the battery7.

The different modes comprise a first mode1corresponding to a normal state mode, a second mode2corresponding to a limit state mode, a third mode3corresponding to an alert state mode, a fourth mode4corresponding to a reserve mode and a fifth mode5corresponding to a security mode.

The alert state mode3is used in case of an abnormal event occurring in the power grid1such as a power plant breakdown. In the reserve mode, the adaptation of the setpoint Sp and/or the gain setting K are stopped until the state of charge SoC returns to the normal state mode. The security mode has to be avoided to avoid damages of the battery7. The goal of the management of the battery7is to adapt the values of the setpoint Sp and the gain setting K to keep the battery in the normal state mode as much as possible.

Different strategies may be set up to ensure the management of the battery7. One example will be given in the following of the description but other strategies may also be applied to adapt the values of the setpoint Sp and/or the gain setting K according to the variations of the frequency f and the state of charge SoC of the battery7.

a) Normal State Mode10

In the normal mode10, the gain setting K varies between an upmost value, herein 25, and a lowermost value, herein 5.

During a charge of the battery7represented in solid line inFIG.5, the gain setting K is set to the upmost value 25 when the state of charge SoC is low, close to the lower limit NL of the normal state mode10, and is set to the lowermost value 5 when the state of charge is high, close to the upper limit NH of the normal state mode10.

During a discharge of the battery7represented in dashed line inFIG.5, the gain setting K is set to the lowermost value 5 when the state of charge is low, close to the lower limit NL of the normal state mode10, and is set to the uppermost value 25 when the state of charge is high, close to the upper limit of the normal state mode10.

A higher value of the gain setting K produces a higher response of the battery7to a variation of the frequency f with respect to the nominal frequency fn.

The setpoint Sp varies between 2 extreme values, for example between an high extreme value 0.25 and a low extreme value −0.25 as represented inFIG.6. The 0.25 and −0.25 are normalized values which refer to a setpoint Sp associated with a unitary power Pa engaged for power grid stabilization (for a power Pa of 20MW as described previously, the setpoint associated with the normalized value of 0.25 will be 5 MW (20 MW*0.25)).

A high positive value of the setpoint Sp promotes the charge of the battery7and a low negative value of the setpoint Sp promotes a discharge of the battery7.

Indeed, the setpoint Sp acts as an offset for the total power Pt of the battery7so that if the setpoint is set of 5 MW, 5 MW will be injected in the power grid1independently of the power Pa engaged for power grid stabilization. Thus, if at a given instant, the power Pa engaged for power grid stabilization is 2 Mw, the total power Pt of the battery7will be 5 MW−2 MW=3 MW. As a consequence, at this given instant, the battery7will be charging despite the fact that the power grid1requires a discharge of the battery7.

b) Limit State Mode11

In the high limit state mode noted HLS inFIG.4, the gain setting K is set to the lowermost value 5 during a charge of the battery7and is set to the upmost value 25 during a discharge of the battery7.

In this high limit state mode HLS, the setpoint SP is set to the low extreme value, for example −0.25.In the low limit state mode noted LLS inFIG.4, the gain setting K is set to the upmost value 25 during a charge of the battery7and is set to the lowermost value 5 during a discharge of the battery7.In this low limit state mode LLS, the setpoint Sp is set to the high extreme value, for example 0.25.

c) Alert State Mode12

In the high alert state mode noted HAS inFIG.4, the gain setting K is set to the lowermost value 5 during a charge of the battery7and is set to the upmost value 25 during a discharge of the battery7.

In this high alert state mode HAS, the setpoint Sp is set to the low extreme value −0.25.In the low alert state mode noted LAS inFIG.4, the gain setting K is set to the upmost value 25 during a charge of the battery7and is set to the lowermost value 5 during a discharge of the battery7.In this low alert state mode LAS, the setpoint Sp is set to the high extreme value 0.25.

d) Reserve Mode13

In the reserve mode, the frequency sensitive mode described above is suspended. In both the high and low reserve modes13, the gain setting K and the setpoint Sp are set to 0 until the power grid1returns to its normal state.When the power grid1returns to its normal state, if the state of charge SoC of the battery7is low, the battery7sets a constant setpoint Sp of charge during two hours to return to a state of charge SoC of 50% and if the state of charge SoC is high, the battery7sets a constant setpoint Sp of discharge during two hours to return to a state of charge SoC of 50%.

e) Security Mode14

The strategy prevents from entering the security mode14.

As indicated previously, other management may be set up, for example, only the setpoint Sp may vary according to the state of charge SoC of the battery7and the variations of the frequency while the gain setting K remains constant or alternatively, only the gain setting K may vary according to the state of charge SoC of the battery7and the variations of the frequency while the setpoint Sp remains constant.

Indeed, the variations of the gain K and the setpoint Sp between the lower limit and the upper limit are not necessarily as represented inFIG.5andFIG.6and in particular not necessarily linear.

According to a first alternative, the gain K may be set to the lowermost value 5 (independently of the state of charge SoC) and the setpoint Sp may vary linearly until the state of charge SoC reaches a threshold corresponding to a predetermined percentage before reaching the alert state mode, for example 5% before reaching the alert state mode and may be set to the high extreme value above this threshold.

According to a second alternative, the gain K is set to the lowermost value 5 when the state of charge SoC lies within a range from 45% to 55%, varies linearly from 5 to 7.5 otherwise and is set to the uppermost value when the alert state mode is reached.

According to a third alternative, the gain K is set to the lowermost value 5 and the setpoint Sp varies as a sinusoidal function (sin(X*(π/2)) with X the difference with the percentage of charge from a 50% charge) and is set to the uppermost value when the alert state mode is reached.

Other laws can be applied for the gain K and the setpoint Sp in order to compensate for the frequency variations.

These managements are set up at predetermined time intervals of at least 15 minutes. A high number of batteries7may be managed with such strategy in order to enable stabilization of the power grid1.

Thus, such management of the battery7based on the adaption of the gain setting K associated with a power engaged for grid stabilization and/or of the setpoint Sp of a power associated with the management of the state of charge SoC of the battery7enables absorbing frequency variations of the power grid1around the nominal frequency fn and therefore provide a stabilization of the power grid1. Such management may also enable facing a breakdown of a source3of the network such as a power plant breakdown.