Method and control device for operating a stationary, electric energy storage that is provided for an electric consumption unit

Abstract

A method operates an electric energy storage that is provided for an electric consumption unit, wherein the electric consumption unit is additionally coupled to an electric power grid. The method is characterized in that the control device performs the following steps of a) providing different operation logics for controlling the power flow as a function of the state of charge and of a total unit load, b) observing a status signal that is signaling the present and/or the next supply condition of the grid, c) selecting one of the operation logics as an active operation logic depending on a current value of the status signal, and d) operating the power converter according to the active operation logic.

Claims

1. A method for operating an electric energy storage that is provided for an electric consumption unit, wherein the electric consumption unit is additionally coupled to an electric power grid and wherein the grid supplies electric power to the consumption unit under different supply conditions at different time periods and wherein a control device observes a state of charge of the energy storage and controls an electric power flow of the energy storage by way of an electric power converter, the method comprising the steps of: providing different operation logics for controlling power flow as a function of the state of charge and a function of a total unit load, wherein the total unit load is a net balance value of a power consumption in the consumption unit and an internal power delivery in the power consumption unit; observing a status signal that is signaling a present and/or a next supply condition of the grid; selecting one of the operation logics as an active operation logic depending on a current value of the status signal; operating the power converter according to the active operation logic, wherein one of the supply conditions is a demand-response supply condition which is valid during demand-response periods and one of the supply conditions is a pre-event supply condition which is valid during pre-event periods each of which immediately precedes a respective demand-response period, and for the pre-event supply condition a pre-event operation logic is selected, which pre-event operation logic comprises: if a time duration remaining until the end of the present pre-event period is shorter than or equal to a predefined stretched Final Charge Window, a positive power flow for charging the energy storage is set to a scaled value which is calculated such that the state of charge reaches a maximum level at the end of the pre-event period.

2. The method according to claim 1, wherein a Final Charge Window is a time value needed for charging the energy storage from its present state of charge to a maximum level, if a maximum converter power of the power converter is used, and the stretched Final Charge Window is the Final Charge Window multiplied by a stretch factor α, with a greater than or equal to 1, wherein the scaled value is the maximum converter power divided by the stretch factor α.

3. The method according to claim 1, wherein for the pre-event operation logic: if the time duration remaining until the end of the present pre-event period is greater than the stretched Final Charge Window, and the total unit load is greater 0, indicating a net power consumption, the power flow for charging the energy storage is set to 0 independently of the state of charge, and otherwise, if the total unit load is smaller 0, indicating a net power delivery, a positive power flow is set for charging the energy storage, if the state of charge is below maximum value.

4. The method according to claim 1, wherein for the demand-response supply condition, a demand-supply operation logic is applied, which demand-supply operation logic comprises: if the total unit load is greater 0, indicating a net power consumption, and the state of charge is greater than a predefined demand-response threshold, a negative power flow is set for discharging the energy storage, if the total unit load is smaller 0, indicating a net power delivery, and either the state of charge is at a predefined maximum level or the state of charge is below the maximum level and net energy metering applies, the power flow is set to 0, otherwise, if the total unit load is smaller 0, indicating a net power delivery, a positive power flow is set for charging the energy storage.

5. The method according to claim 1, wherein for a non-event period, when neither the pre-event period nor the demand-response period applies, a non-event operation logic is applied, which non-event logic comprises: if the total unit load is greater 0, indicating a net power consumption, and the state of charge is greater than a predefined demand-response threshold, a negative power flow is set for discharging the energy storage, if the total unit load is smaller 0, indicating a net power delivery, and the state of charge is at the maximum level, the power flow is set to 0, otherwise, if the total unit load is smaller 0, a positive power flow is set for charging the energy storage.

6. The method according to claim 1, wherein an absolute value of the power flow is limited by both a maximum converter power of the power converter and an absolute value of the total unit load.

7. A control device for controlling an electric power flow of an electric energy storage, wherein the control device comprises a processing unit operatively configured to carry out the acts of: providing different operation logics for controlling the power flow as a function of the state of charge and a function of a total unit load, wherein the total unit load is a net balance value of a power consumption in the consumption unit and an internal power delivery in the consumption unit; observing a status signal that is signaling a present and/or a next supply condition of the grid; selecting one of the operation logics as an active operation logic depending on a current value of the status signal; operating the power converter according to the active operation logic, wherein one of the supply conditions is a demand-response supply condition which is valid during demand-response periods and one of the supply conditions is a pre-event supply condition which is valid during pre-event periods each of which immediately precedes a respective demand-response period, and for the pre-event supply condition a pre-event operation logic is selected, which pre-event operation logic comprises: if a time duration remaining until the end of the present pre-event period is shorter than or equal to a predefined stretched Final Charge Window, a positive power flow for charging the energy storage is set to a scaled value which is calculated such that the state of charge reaches a maximum level at the end of the pre-event period.

8. A system, comprising: an electric consumption unit; an electric energy storage; a power converter by which electric power flows to/from the energy storage; and a control device, wherein the control device comprises a processing unit operatively configured to carry out the acts of: providing different operation logics for controlling the power flow as a function of the state of charge and a function of a total unit load, wherein the total unit load is a net balance value of a power consumption in the consumption unit and an internal power delivery in the consumption unit; observing a status signal that is signaling a present and/or a next supply condition of the grid; selecting one of the operation logics as an active operation logic depending on a current value of the status signal; operating the power converter according to the active operation logic, wherein one of the supply conditions is a demand-response supply condition which is valid during demand-response periods and one of the supply conditions is a pre-event supply condition which is valid during pre-event periods each of which immediately precedes a respective demand-response period, and for the pre-event supply condition a pre-event operation logic is selected, which pre-event operation logic comprises: if a time duration remaining until the end of the present pre-event period is shorter than or equal to a predefined stretched Final Charge Window, a positive power flow for charging the energy storage is set to a scaled value which is calculated such that the state of charge reaches a maximum level at the end of the pre-event period.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic illustration of a system according to an embodiment of the invention.

(2) FIG. 2 is a diagram illustrating different time periods during which different supply condition apply for the case of a Demand Response scheme.

(3) FIG. 3 is a flowchart of a method that may be performed by a control device of the system of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) The embodiments explained in the following is a preferred embodiment of the invention. However, in the embodiment, the described components of the embodiment each represent individual features of the invention which are to be considered independently of each other and which each develop the invention also independently of each other and thereby are also to be regarded as a component of the invention in an individual manner or in another than the shown combination. Furthermore, the described embodiment can also be supplemented by further features of the invention already described.

(5) In the figures, identical reference signs respectively indicate elements that provide the same functionality.

(6) FIG. 1 illustrates a system 10 that may comprise an electric consumption unit 11 and an electric energy storage 12 that may be provided for the electric consumption unit 11. The electric consumption unit 11 may be, for example, a household or an office building. In the following, it may be assumed that the energy storage 12 may comprise at least one rechargeable battery. For the sake of simplicity, it may be assumed that the electric consumption unit is a household.

(7) The consumption unit 11 may be connected to an electric power grid 13. By means of the power grid 13, electric power POW may be transferred from, e.g., an electric power plant (for example a nuclear power plant) to the consumption unit 11. The consumption unit 11 may be connected to grid 13 together with other consumption units. The connection of consumption unit 11 may be obtained by means of a meter 14 which may measure the amount of electric energy provided to the consumption unit 11.

(8) Within consumption unit 11, at least one electric consumer 15 may consume electric energy resulting in electric power consumption 16. Additionally, a regenerative energy source 17 may be provided. Energy source 17 represents all electric sources that may provide renewable electric energy. The energy source 17 may comprise at least one photovoltaic solar device 18 and/or at least one electric generator driven by wind. The regenerative energy source 17 may provide an electric power delivery 20. By means of the power delivery 20, the power consumption 16 may be at least partially compensated resulting in an overall net balance value which is termed here as total unit load THL describing, e.g., a total household load.

(9) An electric power flow BP into the energy storage 12 may be controlled by way of a power converter 21 which can be, e.g., an electric inverter, particularly a bidirectional inverter. In the present description, a positive power flow BP indicates the transfer of electric energy into the energy storage, i.e. a charge CHRG, wherein a negative power flow BP indicates a discharge DIS off energy out of the energy storage 12. The converter 21 may be connected to the energy consumption unit 11 or it may directly be connected to grid 13, which is indicated in FIG. 1 by use of dashed lines. In the case that the converter 21 is directly connected to grid 13, an energy flow between inverter 21 and grid 13 may also be considered by meter 14 or by the utility provider of grid 13.

(10) The converter 21 may be controlled by a control device 22 which may comprise a processing unit 23 for generating a control signal 24 for controlling converter 21. Control device 22 may observe a state of charge SOC of energy storage 12 and the total unit load THL. Additionally, control device 22 may receive a status signal DR which indicates a present supply condition C1, C2, C3 and/or a future (upcoming) supply condition, as it may be provided by grid 13. The possible supply conditions C1, C2, C3 are explained in connection with FIG. 2.

(11) FIG. 2 illustrates how non-Time-of-Use Rate tariffs may apply over time t. At least one of the following phases may occur, each of which may be signaled by a predefined value of a status signal DR: a demand-response phase Pdr (DR=2, supply condition C3), a pre-event phase Ppe (DR=1, supply condition C2) and/or a non-event phase Pne (DR=0, supply condition C1). The values of DR are to be understood as being exemplary. FIG. 2 shows an example demand-response structure, wherein a possible time-order of different periods may be: a non-event period Pne, a pre-event period Ppe and a demand-response-period Pdr. Each demand-response period may be followed by a nonevent period Pne, again.

(12) FIG. 3 illustrates a flowchart of an algorithm logic for the non-time-of-use based tariffs, when the demand-response structure of FIG. 2 may apply. The flowchart starts at the respective current time t (S0). The algorithm may comprise several operation logics 25, i.e. a pre-event operation logic 29, a demand-response operation logic 30 and a non-event operation logic 31. As the demand-response operation logic 30 and the non-event operation logic 31 are very similar, they are represented by a common section of the flowchart in FIG. 3. They are distinguished by the condition DR=2 that must additionally (“&&”) apply (indicating demand-response operation logic 30).

(13) In the flowchart shown here, a “+”-Sign indicates “True” for the respective preceding logical test, and a “−”-Sign indicates “False”.

(14) Non-time-of-use rates, such as flat rates or tiered tariffs, do not have periods of time-based price differentials, therefore, it does not matter at what time of the day electricity is drawn from the grid 13. The goal of the energy storage control algorithm on this type of electricity rate tariff is to consume as much renewable energy onsite as possible, such as from solar generation. Therefore, if the customer has solar panels at his/her household or any regenerative energy source 17, then anytime there is excess energy generation and the energy storage 12 is not fully charged, the operation logic will recharge the energy storage 12 using this excess energy generation (THL<0). However, if there is never any excess energy generation e.g. from the solar panels after meeting onsite demand, the energy storage 12 would never get recharged.

(15) Therefore, when the Total Unit Load (THL) is positive and there is no battery capacity remaining, electricity will be drawn from the grid in order to meet onsite loads. Since the price of electricity is the same regardless of the time of day, it does not make a cost difference to charge the battery from the grid in order to provide it to onsite loads at a later time. Additionally, doing so would create efficiency losses.

(16) However, if the user is part of a Demand Response type program, such that the consumption unit 11 receives either a price penalty for consuming electricity during a certain period or a credit for not consuming electricity during a certain period, typically on the order of hours, (supply condition C3), the battery control algorithm as shown in FIG. 3 will operate the energy storage 12 similarly to that of a customer on a time-of-use tariff. The algorithm logic will check first whether there is an upcoming Demand Response event (supply condition C2, DR=1 indicates upcoming supply condition C3) and if so, the Demand Response trigger is set to “pre-event” mode (Ppe).

(17) A Final Charge Window FCW is calculated as the remaining time before the higher-priced period begins (supply condition C3), such as a Demand Response period Pdr. Only in this case would the energy storage 12 recharge from the grid. However, in order to consume as much renewable energy onsite as possible and to reduce consumption of electricity from the utility grid, the energy storage 12 will wait to do so until the time remaining to fully recharge the energy storage 12 has exceeded the available time left before the Demand Response period (scaled FCW, i.e. α*FCW).

(18) The Final Charge Window (FCW) is the calculation of the remaining charging time with maximum charging power. For energy storage safety reasons this timeframe can be stretched in order to charge the battery with a lower rate to minimize harm to the energy storage. This is provided by the stretch factor α which extends the charging window by dividing the maximum battery charging power (InvMaxPower) according to the following relation:
T≤α*FCW then effective Inverter Charging Power is InvMaxPower/α with α≥1 and α a real number.

(19) If the remaining available time T until the next partial peak or peak period is longer than α*FCW, the energy storage 12 will be charged from excess solar only, when available. This logic ensures that there will be as much solar energy as possible in the energy storage 12. Alternatively, if the available time until the next partial peak or peak period is less than α*FCW, the energy storage 12 will be charged from the grid when there is no excess solar available to ensure that the energy storage 12 is fully charged before the next higher-priced period. Even if there is excess renewable energy (solar) available, the energy storage will be charged by InvMaxPower/alpha. It is possible that the energy storage 12 is going to be charged partially from excess renewable energy (solar) and additional grid power POW, if the generation of excess renewable energy (solar) is less than the needed charging power for meeting the requirements to meet the FCW time.

(20) In this way, the energy storage 12 will attempt to charge with as much renewable energy as possible. After the energy storage 12 is fully recharged and the Demand Response event or higher price period has begun, the Demand Response trigger is set to “active” mode, allowing the energy storage 12 to discharge to onsite loads during this higher-priced period or charge from excess renewable energy if the customer is not eligible for a NEM tariff. If it is the case that the customer is eligible for a NEM tariff, instead of recharging the energy storage 12 from excess renewable energy (e.g. solar energy), it is more economically beneficial to feed the excess renewable energy back to the grid rather than storing it in the energy storage 12.

(21) The described methodology takes into account the specific utility rate tariffs and combines the use cases of energy arbitrage with solar self-consumption to find the cycling algorithm that provides the most cost savings for the user.

(22) The implementation example shows, how an energy storage 12 cycling algorithm for a stationary storage system in a residential environment can be provided.

REFERENCE SIGNS

(23) 10 system 11 electric consumption unit 12 energy storage 13 power grid 14 meter 15 electric consumer 16 power consumption 17 regenerative energy source 18 photovoltaic panel 19 wind generator 20 power delivery 21 power converter 22 control device 23 processing unit 24 control signal 25 operation logic 30 demand-response operation logic 31 non-event operation logic C costs C1, C2, C3 supply condition BP power flow BTHdr demand-response threshold DR status signal NEM net energy metering InvMaxPower maximum converter power POW electric power Pne non-event period Ppe pre-event period Pdr demand-response period SOC state of charge t time THL total unit load

(24) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.