A charge-discharge collaborative scheduling method of a photovoltaic energy storage system

Abstract

The application relates to the technical field of photovoltaic energy storage system operation control, and discloses a charging and discharging collaborative scheduling method of a photovoltaic energy storage system. In response to a live transfer request in a double-transformer split-column operation state, a line to be withdrawn and a reserved line are determined, and transfer power data are acquired; energy storage support power to be maintained and energy storage units on a support side and a compensation side are determined; support power exposure and pre-compensation demand are determined in combination with equivalent impedance of a transformer; when a bus coupler switch is opened, the energy storage unit on the compensation side is adjusted, effective compensation power is determined according to actual power change, and the bus coupler switch is closed when the effective compensation power reaches the pre-compensation demand and the transformer on the compensation side is not out of limit. The application can reduce the risk of bus active power out of limit caused by energy storage support power.

Description

Technical Field

[0001] This application relates to the field of photovoltaic energy storage system operation control technology, and in particular to a method for coordinated scheduling of charging and discharging of photovoltaic energy storage systems. Background Technology

[0002] In a power distribution system with two transformers and two busbars, the two transformers typically supply power to their respective busbars, and a bus tie switch is installed between the two busbar sections. To maintain one of the transformers or adjust the power supply mode, a live-line transfer method can be used. First, the bus tie switch is closed, allowing the two transformers to supply power in parallel for a short period, and then the incoming line to be disconnected is disconnected to reduce power outages. With distributed photovoltaic (PV) and energy storage units connected to both busbar sections, the active power of the incoming lines to the two transformers is affected not only by load changes but also by variations in PV output and the charging and discharging power of the energy storage units, making the power distribution after the bus tie switch more complex.

[0003] Before live-line power transfer begins, an energy storage unit may have already regulated the incoming active power of the transformer corresponding to its busbar by charging or discharging to keep it within the allowable power range. For example, when the load power is high, the energy storage unit can discharge to reduce the incoming active power borne by the transformer; when the photovoltaic power is high, the energy storage unit can charge to suppress reverse power transmission. Therefore, the energy storage unit cannot directly exit its original charging / discharging state during live-line power transfer, otherwise it may cause the corresponding transformer to overload or exceed the reverse power limit. However, after the two busbars are connected via the bus tie switch, the energy storage power that originally only acted on a single busbar will be redistributed according to the impedance of the two transformers and the power state of the two busbars. Some of the energy storage power may be converted into active power flowing through the bus tie switch, resulting in an increase in the bus tie power.

[0004] Existing photovoltaic energy storage systems typically determine the charging and discharging commands of energy storage units based on transformer load rate, photovoltaic power, load power, or energy storage state of charge. Live-line power transfer control primarily relies on the voltage, frequency, and phase angle on both sides of the bus tie switch to determine whether closing is permitted. These two types of control are usually independent, making it difficult to identify the non-removable support power of the energy storage unit to maintain the transformer's incoming power safety. Furthermore, they do not fully consider the potential impact of communication delays, power change rates, and operating conditions on the actual charging and discharging power of the energy storage converter after receiving regulation commands.

[0005] Therefore, how to prevent the active power of the bus tie from exceeding the limit after the bus tie is turned off while maintaining the original energy storage support function is a technical problem that needs to be solved when the photovoltaic energy storage system is used for live power transfer. Summary of the Invention

[0006] The purpose of this application is to provide a method for coordinated charging and discharging of a photovoltaic energy storage system, so as to maintain the original supporting role of the energy storage unit on the corresponding transformer during the energized power transfer process of the dual transformers, and reduce the risk of the active power of the bus tie caused by the energy storage supporting power exceeding the limit after the bus tie is closed.

[0007] According to one aspect of this application, a method for coordinated charging and discharging of a photovoltaic energy storage system is provided. The photovoltaic energy storage system includes a first transformer and a second transformer that supply power to a first busbar and a second busbar respectively via a first incoming line and a second incoming line. The first busbar and the second busbar are connected via a bus tie switch, and each of the two busbar segments is connected to a photovoltaic branch, a load branch, and an energy storage unit. The method includes:

[0008] In response to the request for live power transfer when the first transformer and the second transformer are operating separately, the incoming line to be withdrawn and the reserved incoming line are determined from the first incoming line and the second incoming line, and the active power of the incoming lines of the two transformers, the photovoltaic power and load power of the two bus sections, and the actual charging and discharging power of the two energy storage units are obtained. The obtained power data are determined as the power transfer data.

[0009] Based on the relationship between the active power of the incoming lines and the allowable power range of the two transformers, the energy storage support power that needs to be maintained during the live power transfer period from the closing of the bus tie switch to the withdrawal of the incoming line is determined. The energy storage unit that provides the energy storage support power is determined as the support side energy storage unit, and the other energy storage unit is determined as the compensation side energy storage unit.

[0010] Based on the busbar where the supporting energy storage unit is located, the incoming line to be withdrawn and the retained incoming line, the equivalent impedance of the two transformers, and the power transfer data, determine the amount of supporting power exposure that maintains the energy storage supporting power relative to the increase in the absolute value of the bus coupler active power caused by the closing of the bus coupler switch, and determine the pre-compensation requirement that ensures the absolute value of the predicted active power of the bus coupler does not exceed the bus coupler active power limit when maintaining the energy storage supporting power.

[0011] With the bus tie switch kept open, the compensation-side energy storage unit is controlled to adjust the actual charging and discharging power, and the effective compensation power that can reduce the absolute value of the bus tie active power after the bus tie switch is closed is determined based on the change in the actual charging and discharging power of the compensation-side energy storage unit relative to the amount of change in the actual charging and discharging power before the power adjustment begins.

[0012] When the effective compensation power reaches the pre-compensation requirement, and the active power of the incoming line of the transformer connected to the same bus as the compensation-side energy storage unit is within the corresponding allowable power range, a closing control signal is sent to the bus tie switch.

[0013] This application has the following beneficial effects:

[0014] This application determines the energy storage support power required during live-line power transfer based on the relationship between the active power of the incoming lines of the two transformers and their respective allowable power ranges, and distinguishes between the support-side energy storage units and the compensation-side energy storage units. Based on the equivalent impedance and power transfer data of the two transformers, it determines the exposure of the energy storage support power after the bus tie switch is closed and the pre-compensation requirements. With the bus tie switch remaining open, the compensation-side energy storage units are controlled to adjust their actual charging and discharging power. The condition for bus tie-off is that the actual effective compensation power reaches the pre-compensation requirements and the active power of the incoming lines of the compensation-side transformer does not exceed the allowable power range. Therefore, while maintaining the original energy storage support function, it can reduce the risk of the bus tie active power exceeding the limit after bus tie-off and reduce the impact of the actual power response deviation of the energy storage units on live-line power transfer control. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the electrical topology of a photovoltaic energy storage system according to one embodiment of this application.

[0017] Figure 2 This is a schematic flowchart of the charging and discharging coordinated scheduling method for a photovoltaic energy storage system according to an embodiment of this application.

[0018] Explanation of icon numbers:

[0019] 1. First transformer; 2. Second transformer; 5. First busbar; 6. Second busbar; 7. Bus tie switch; 8. First photovoltaic branch; 9. Second photovoltaic branch; 10. First load branch; 11. Second load branch; 12. First energy storage unit; 13. Second energy storage unit; 14. First incoming switch; 15. Second incoming switch. Detailed Implementation

[0020] The embodiments of this application will be described in detail below. It should be understood that the following embodiments are used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Where there is no conflict, the technical features of the various embodiments of this application can be combined with each other.

[0021] Please see Figure 1 and Figure 2 This application provides a method for coordinated charging and discharging scheduling of a photovoltaic energy storage system, according to one embodiment. See also...Figure 1 The photovoltaic energy storage system includes a first transformer 1, a second transformer 2, a first busbar 5, a second busbar 6, and a bus tie switch 7. The first transformer 1 is connected to the first busbar 5 via a first incoming line and a first incoming line switch 14. The second transformer 2 is connected to the second busbar 6 via a second incoming line and a second incoming line switch 15. The first busbar 5 and the second busbar 6 are connected via the bus tie switch 7. The first busbar 5 is connected to a first photovoltaic branch 8, a first load branch 10, and a first energy storage unit 12. The second busbar 6 is connected to a second photovoltaic branch 9, a second load branch 11, and a second energy storage unit 13.

[0022] Both the first energy storage unit 12 and the second energy storage unit 13 may include an energy storage battery, an energy storage converter, and an energy storage controller. The energy storage controller controls the corresponding energy storage converter to perform charging or discharging regulation according to the received power regulation command. The first incoming line, the second incoming line, the bus tie switch 7, the two photovoltaic branches, the two load branches, and the two energy storage units may each be equipped with a power detection device. The energy management controller implementing this method is communicatively connected to each power detection device, the energy storage controller, the first incoming line switch 14, the second incoming line switch 15, and the bus tie switch 7 to obtain power data and switch status, and output energy storage power regulation commands and switch control signals.

[0023] In this embodiment, the direction in which the first transformer 1 or the second transformer 2 supplies active power to the corresponding busbar is defined as the positive direction of incoming active power; the direction in which the first busbar 5 supplies active power to the second busbar 6 via the bus tie switch 7 is defined as the positive direction of bus tie active power; and the direction in which the energy storage unit discharges to its respective busbar is defined as the positive direction of energy storage active power. When the energy storage unit absorbs active power from its respective busbar for charging, its actual charging and discharging power is negative. Both photovoltaic power and load power are expressed as the absolute power values ​​of the corresponding branches.

[0024] The net injected power of the i-th bus segment can be determined according to the following formula:

[0025] PINi = PPVi + PESi - PLi;

[0026] Wherein, PINi is the net injected power of the i-th bus segment, PLi is the load power of the bus segment, PPVi is the photovoltaic power of the bus segment, and PESi is the actual charging and discharging power of the energy storage unit connected to the bus segment. i is either 1 or 2. A positive net injected power indicates that the bus segment as a whole has a tendency to output active power to the transformer or another bus segment, while a negative net injected power indicates that the bus segment as a whole needs to obtain active power from the transformer or another bus segment.

[0027] To better represent the power demand of the busbar, the net power consumption of the i-th busbar segment can also be denoted as PNi, where PNi = -PINi, i.e.:

[0028] PNi = PLi-PPVi-PESi.

[0029] A positive net power consumption value indicates that the busbar segment as a whole needs to draw active power from the transformer or another busbar segment, while a negative net power consumption value indicates that the busbar segment has a tendency to output active power to the transformer or another busbar segment. Subsequent power flow calculations using net injected power or net power consumption in the opposite direction yield substantially the same results.

[0030] The permissible power range for each transformer may include a lower limit for permissible reverse active power and an upper limit for permissible forward active power. The permissible power range can be determined based on the transformer's rated capacity, permissible load rate, short-time overload capacity, reverse power protection settings, and photovoltaic grid-connected operation requirements. For systems with short-time parallel operation capabilities, separate permissible power ranges for split operation and short-time parallel operation can be set. Unless otherwise stated, the permissible power range described herein refers to the permissible power range corresponding to the current power determination operating phase; the split operation permissible power range is used during the split operation phase, and the short-time parallel operation permissible power range is used during the short-time parallel power supply phase of two transformers.

[0031] In this embodiment, the energy storage support power Psup represents the amount of power required to maintain the active power of the corresponding transformer's incoming line within the allowable power range; Psup is a non-negative value. The energy storage support direction indicates whether the energy storage support power corresponds to the charging or discharging direction. The change in energy storage support power including direction is denoted as ΔPESs. When the energy storage support direction is the discharging direction, ΔPESs is a positive value; when the energy storage support direction is the charging direction, ΔPESs is a negative value, and |ΔPESs|=Psup.

[0032] See Figure 2 The charging and discharging coordinated scheduling method described in this embodiment includes steps S10 to S50.

[0033] In step S10, in response to the live power transfer request under the separate operation state of the first transformer 1 and the second transformer 2, the incoming line to be withdrawn and the incoming line to be reserved are determined, and the power transfer data is acquired and generated.

[0034] Live-line power transfer requests can be input by operators through a dispatch terminal, or automatically generated based on transformer maintenance plans, incoming line anomaly warnings, or power supply mode adjustment plans. A live-line power transfer request must include at least the identification information of the transformer or incoming line that needs to be taken out of operation. The energy management controller uses this identification information to identify the corresponding incoming line as the line to be taken out, and designates the other incoming line as the reserved incoming line. For example, when it is necessary to take out the second transformer 2, the second incoming line is designated as the line to be taken out, and the first incoming line is designated as the reserved incoming line.

[0035] When a power transfer request is generated, both the first incoming line switch 14 and the second incoming line switch 15 are in the closed position, the bus tie switch 7 is in the open position, and the first transformer 1 and the second transformer 2 are electrically connected to their respective busbars. The energy management controller acquires the active power of the incoming lines of the first transformer 1 and the second transformer 2, the photovoltaic power of the first photovoltaic branch 8 and the second photovoltaic branch 9, the load power of the first load branch 10 and the second load branch 11, and the actual charging and discharging power of the first energy storage unit 12 and the second energy storage unit 13, and determines the acquired power data as the power transfer data.

[0036] Each power data point can carry the sampling time. The energy management controller can group data with sampling times within the same preset synchronization time window into a set of power transfer data, avoiding the use of data from different times due to changes in photovoltaic output or load. For rapidly changing photovoltaic power or load power, the average or median value over multiple consecutive sampling periods can be used as the current power. When any necessary data exceeds the preset valid time limit, the data quality flag is abnormal, or the change between multiple consecutive sampling values ​​exceeds the corresponding mutation threshold, the current power transfer process can be paused, and the power transfer data can be reacquired.

[0037] In step S20, based on the relationship between the active power of the incoming lines of the two transformers and the allowable power range, the energy storage support power that needs to be maintained during the live power transfer period is determined, and the support-side energy storage unit and the compensation-side energy storage unit are determined.

[0038] Energy storage support power refers to the charging or discharging power that an energy storage unit cannot directly remove during live-line power transfer in order to keep the active power of the transformer connected to its bus within the allowable power range. Energy storage support power is not necessarily equal to the total actual charging and discharging power of the energy storage unit. For example, in addition to performing transformer incoming power limiting tasks, an energy storage unit can simultaneously perform planned charging and discharging or photovoltaic power consumption tasks; the power that must be retained to meet the transformer incoming power limits constitutes the energy storage support power.

[0039] The energy management controller analyzes the changes in the actual charging and discharging power of the two energy storage units relative to their corresponding non-supporting reference power, and predicts the incoming active power of the corresponding transformer after the change is removed. When the predicted incoming active power of one transformer exceeds the allowable power range, while the predicted incoming active power of the other transformer remains within the allowable power range, the energy storage unit corresponding to the former transformer is designated as the supporting-side energy storage unit, the charging or discharging power to be retained is designated as the energy storage support power, and the other energy storage unit is designated as the compensation-side energy storage unit.

[0040] If removing the corresponding energy storage power from both transformers will not exceed the allowable power range, the energy storage support power can be set to zero, and conventional live power transfer can be performed when other power transfer conditions are met. If removing the corresponding energy storage power from both transformers will exceed the allowable power range, it indicates that both energy storage units are undertaking support tasks that cannot be directly removed, and there is no side between the two existing energy storage units that can directly serve as a compensation-side energy storage unit. In this case, the energy management controller can stop the current bus stop closing process, output insufficient power transfer conditions, or first restore one of the transformers to the allowable power range by reducing unnecessary loads, limiting photovoltaic output, or adjusting other controllable power sources.

[0041] In step S30, the power exposure and pre-compensation requirements are determined based on the bus where the energy storage unit is located, the incoming line to be withdrawn and the reserved incoming line, the equivalent impedance of the two transformers, and the power transfer data.

[0042] When the two transformers are operating separately, the charging and discharging power of the energy storage unit on the support side primarily affects the transformer connected to the same busbar. After the bus tie switch 7 is closed, the two transformers and two busbar sections form a parallel power supply network. The power changes of the energy storage unit on the support side will be redistributed according to the equivalent impedance of the two transformers and the power status of the two busbar sections, causing changes in the active power of the bus tie. Therefore, the energy management controller calculates the bus tie baseline predicted active power without considering the energy storage support power and the bus tie support predicted active power while maintaining the energy storage support power.

[0043] The amount of supporting power exposure can be determined by the following formula:

[0044] Pexp=max(0,|PMsup|-|PM0|);

[0045] Where Pexp is the supporting power exposure, PM0 is the bus coupler baseline predicted active power, and PMsup is the bus coupler supporting predicted active power. Supporting power exposure is only generated when the energy storage supporting power increases the absolute value of the bus coupler predicted active power; when the energy storage supporting power decreases the absolute value of the bus coupler predicted active power, the supporting power exposure is zero.

[0046] The pre-compensation requirement can be determined according to the following formula:

[0047] Ppre=max(0,|PMsup|-PMlim);

[0048] Where Ppre represents the pre-compensation demand and PMlim represents the bus tie active power limit. When the absolute value of the predicted active power supported by the bus tie does not exceed the bus tie active power limit, the pre-compensation demand is zero; when the absolute value of the predicted active power supported by the bus tie exceeds the bus tie active power limit, the excess portion constitutes the minimum compensation power that the compensation-side energy storage unit needs to actually generate before the bus tie is closed.

[0049] In step S40, with the bus tie switch 7 remaining open, the compensation-side energy storage unit is controlled to adjust the actual charging and discharging power and determine the effective compensation power.

[0050] The energy management controller determines the target power change and charging / discharging adjustment direction of the energy storage unit on the compensation side based on the direction of the predicted active power from the bus tie support, the pre-compensation demand, and the power transfer coefficient on the compensation side. The bus tie switch 7 remains open during this adjustment process; therefore, the power change of the energy storage unit on the compensation side is primarily reflected in the change of the active power of the transformer connected to the same bus. The energy management controller continuously monitors the active power of the transformer's input line during the adjustment process to prevent the transformer on the compensation side from prematurely exceeding its allowable power range in order to achieve bus tie pre-compensation.

[0051] The energy management controller does not directly regard the target power change sent to the compensation-side energy storage unit as the already formed compensation power. Instead, it re-acquires the actual charging and discharging power of the compensation-side energy storage unit after each power adjustment command is sent. Based on the change in actual charging and discharging power relative to the power adjustment before the start, and in conjunction with the compensation-side power transfer coefficient, it predicts the change in active power of the bus tie after the bus tie switch 7 is closed, and thus determines the effective compensation power.

[0052] The effective compensation power can be determined by the following formula:

[0053] Peff=max(0,|PMsup|-|PMcomp|);

[0054] Where Peff is the effective compensation power, and PMcomp is the bus coupler compensation predicted active power determined based on the actual power change of the compensation-side energy storage units. If the actual power change of the compensation-side energy storage units is in the wrong direction, the actual response is insufficient, or the power change causes the absolute value of the bus coupler predicted active power to increase further, then the corresponding power change will not be included in the effective compensation power.

[0055] In step S50, when the effective compensation power reaches the pre-compensation requirement and the active power of the transformer connected to the same bus as the compensation-side energy storage unit is within the corresponding allowable power range, a closing control signal is sent to the bus tie switch 7.

[0056] The effective compensation power reaches the pre-compensation requirement, which can be equal to or greater than the pre-compensation requirement. To avoid frequent switching between meeting and not meeting the closing conditions due to power measurement fluctuations, this state can be required to be maintained continuously for a preset number of sampling periods. When the pre-compensation requirement is zero, the target power change of the energy storage unit on the compensation side can be set to zero, and a closing control signal can be sent after other closing conditions are met.

[0057] In some implementations, the support power exposure, pre-compensation requirements, and effective compensation power are determined according to the following process.

[0058] The energy management controller establishes a predicted topology after the bus tie switch 7 is closed, based on the correspondence between the incoming lines to be deactivated and the reserved incoming lines and the first bus 5 and the second bus 6, respectively. The predicted topology includes at least the equivalent impedance of the first transformer 1 and the second transformer 2, the net injected power or net power consumption of the two bus sections, the power supply direction of the two transformers, and the positive direction of the active power of the bus tie.

[0059] When calculating the bus coupler baseline predicted active power, only the actual charging and discharging power PESs of the supporting energy storage units is adjusted to PESs-ΔPESs in the prediction model to form a prediction state that does not consider the energy storage support power, without implementing corresponding actual power adjustments for the supporting energy storage units. While keeping other power transfer data unchanged, the bus coupler baseline predicted active power PM0 is calculated through the prediction topology.

[0060] When calculating the predicted active power of the bus tie support, the energy storage support power and support direction that the energy storage unit on the support side needs to maintain are kept in the prediction model, and the predicted active power PMsup of the bus tie support is calculated through the same prediction topology.

[0061] When |PMsup| is greater than |PM0|, the difference between their absolute values ​​is determined as the support power exposure; when |PMsup| is not greater than |PM0|, the support power exposure is determined to be zero. The support power exposure represents the adverse impact of energy storage support power on the bus power load, but it is not directly equivalent to the pre-compensation demand. For example, if the predicted active power of the bus support is increased relative to the bus baseline predicted active power, but still does not reach the bus active power limit, the support power exposure is greater than zero, while the pre-compensation demand remains zero.

[0062] When |PMsup| is greater than PMlim, |PMsup|-PMlim is determined as the pre-compensation requirement; when |PMsup| is not greater than PMlim, the pre-compensation requirement is determined to be zero. In practical applications, a measurement error margin and a power fluctuation margin can be reserved within the rated allowable power of bus tie switch 7, and the operating control value after reserving the margin is determined as the bus tie active power limit.

[0063] When the energy storage unit on the compensation side begins power adjustment, its actual charge / discharge power PESc,0 before adjustment is recorded. During the adjustment process, its current actual charge / discharge power PESc is obtained, and ΔPESc = PESc - PESc,0 is determined as the actual change in charge / discharge power. The sign of ΔPESc determines whether the power change belongs to increased discharge, decreased discharge, increased charging, or decreased charging. Then, based on the power transfer coefficient on the compensation side, the change in the active power of the bus tie caused by this change in actual charge / discharge power is predicted, resulting in the predicted active power PMcomp of the bus tie compensation.

[0064] When |PMcomp| is less than |PMsup|, |PMsup|-|PMcomp| is determined as the effective compensation power; when |PMcomp| is not less than |PMsup|, the effective compensation power is determined as zero. Therefore, even if the energy storage unit on the compensation side receives the target power command, as long as its actual charging and discharging power has not yet changed accordingly, the pre-compensation will not be prematurely determined to be completed.

[0065] In some implementations, the first incoming line is equipped with a first incoming line switch 14, and the second incoming line is equipped with a second incoming line switch 15. After sending a closing control signal to the bus tie switch 7, the energy management controller obtains the closed position status of the bus tie switch 7 and the electrical connection detection result characterizing whether the two ends of the bus tie switch 7 are connected, and determines whether the first bus 5 and the second bus 6 are actually connected based on the two types of information. This can distinguish the abnormal situation where the bus tie switch 7 has generated a closed auxiliary contact signal but the main contacts are not reliably connected.

[0066] When it is determined that the two busbars are actually connected, the actual charging and discharging power, effective compensation power, and actual active power flowing through the bus tie switch 7 of the supporting side energy storage unit are recorded at the moment of actual connection. The difference between the bus tie active power limit and the absolute value of the actual active power of the bus tie at the moment of actual connection is determined as the bus tie residual power margin. When the calculation result is less than zero, the bus tie residual power margin is determined to be zero, and energy storage regulation that may continue to increase the absolute value of the bus tie active power is immediately restricted.

[0067] During the parallel power supply period of the incoming lines to be decommissioned and the retained incoming lines, the energy management controller continuously acquires the active power of the two transformers' incoming lines, the photovoltaic power and load power of the two bus sections, and the actual charging and discharging power of the two energy storage units, and determines the reacquired power data as the current power transfer data. The current effective compensation power is updated based on the change in the actual charging and discharging power of the compensation-side energy storage units relative to the time before the power adjustment began. Then, the supporting power coverage is determined based on the change in the current effective compensation power relative to the actual connection time and the remaining power margin of the bus tie.

[0068] When the active power of the incoming line of the support-side transformer changes, requiring the support-side energy storage unit to further increase its energy storage support power, the absolute increase in the bus tie active power that this increase in support power might cause is first predicted. Only if this increase does not exceed the support power coverage is the support-side energy storage unit allowed to increase its energy storage support power. Therefore, the compensation-side energy storage unit first establishes the bus tie power capacity before allowing the support-side energy storage unit to use that capacity, avoiding the possibility of simultaneous adjustment of two energy storage units or the support-side energy storage unit adjusting first, which could cause a momentary overrun of the bus tie power limit.

[0069] The energy management controller also predicts the power flow after the incoming line to be withdrawn is removed based on the current power transfer data. When the predicted active power of the transformer connected to the retained incoming line is within the corresponding allowable power range, and the absolute value of the predicted active power flowing through the bus tie switch 7 after the incoming line to be withdrawn does not exceed the bus tie active power limit, a trip control signal is sent to the incoming switch corresponding to the incoming line to be withdrawn.

[0070] If, after sending the closing control signal, the actual connection between the two bus sections is not determined within a preset time limit, the energy management controller stops adjusting the support-side energy storage unit in the direction of increasing energy storage support power, but does not directly remove the necessary support power originally borne by the support-side energy storage unit. At the same time, the control compensation-side energy storage unit gradually restores to the actual charging and discharging power before the start of pre-compensation adjustment according to a preset recovery rate, to avoid a sudden change in the active power of the incoming line of the compensation-side transformer caused by the sudden removal of compensation power.

[0071] In some implementations, the energy storage support power is determined according to the following process.

[0072] The energy management controller acquires the actual charging and discharging power of the first energy storage unit 12 and the second energy storage unit 13 at the most recent time that preset support benchmark conditions were met before the power transfer request was generated. The preset support benchmark conditions include that the active power of the transformer connected to the same bus as the energy storage unit is within the corresponding allowable power range, and that the energy storage unit has not adjusted its charging and discharging power due to the active power of the incoming line approaching or exceeding the allowable power range. The actual charging and discharging power at that moment is determined as the non-support benchmark power of the corresponding energy storage unit.

[0073] The most recent time when the preset support baseline conditions were met can be within a preset historical time window before the live-line power transfer request was generated. If there is no time when the conditions are met within the historical time window, the planned energy storage power given by the current operation plan can be used as the non-support baseline power; if the planned energy storage power is also unavailable, the automatic live-line power transfer process should be suspended, and the operators should be asked to confirm the non-support baseline power.

[0074] For any energy storage unit, its current actual charging and discharging power is denoted as PESi, and its non-supported reference power is denoted as PESi,0. Under the split-operation state with the bus tie switch 7 open, the predicted incoming active power after the support removal of the corresponding transformer can be determined according to the following formula:

[0075] PTi,off = PTi + PESi - PESi,0;

[0076] Wherein, PTi is the current incoming active power of the corresponding transformer, and PTi,off is the predicted incoming active power when the corresponding energy storage unit recovers to the non-supported reference power.

[0077] When PTi,off is greater than the upper boundary of the transformer's allowable power range, it indicates that removing the existing energy storage regulation would result in excessive active power in the transformer's forward input, necessitating the maintenance of energy storage support power in the discharge direction. The required energy storage support power can be determined based on the difference between PTi,off and the upper boundary of the allowable power range.

[0078] When PTi,off is less than the lower boundary of the allowable power range, it indicates that removing the existing energy storage regulation would cause the active power of the reverse incoming line to exceed the limit, and it is necessary to maintain the energy storage support power in the charging direction. The required energy storage support power can be determined based on the difference between the lower boundary of the allowable power range and PTi,off.

[0079] When the predicted active power of the incoming line after the support removal of one transformer is outside the allowable power range of that transformer, while the predicted active power of the incoming line after the support removal of another transformer is within the allowable power range of that other transformer, the former is identified as the target transformer, and the energy storage unit corresponding to the target transformer is identified as the support-side energy storage unit. The other energy storage unit is correspondingly identified as the compensation-side energy storage unit.

[0080] The energy management controller determines the expected transfer duration based on the preset operating time limit of bus tie switch 7, the preset parallel power supply time limit, and the preset exit time limit of the incoming switch corresponding to the pending line. For the energy storage support power in the discharge direction, the required dischargeable power can be determined based on the energy storage support power, the expected transfer duration, and the discharge efficiency; for the energy storage support power in the charging direction, the required rechargeable capacity can be determined based on the energy storage support power, the expected transfer duration, and the charging efficiency.

[0081] The available power in this application is determined based on the energy storage support direction. When the energy storage support direction is the discharge direction, the available power is the amount of electricity that the energy storage unit can release under the condition that it is not lower than the minimum permissible state of charge; when the energy storage support direction is the charging direction, the available power is the amount of electricity that the energy storage unit can continue to absorb under the condition that it is not higher than the maximum permissible state of charge.

[0082] When the available power is not less than the required power, the actual charging and discharging power of the energy storage after maintaining the energy storage support power is within the allowable charging and discharging power range of the corresponding energy storage unit, and the energy storage unit can adjust from the current actual charging and discharging power to the actual charging and discharging power that needs to be maintained, it is determined that the energy storage support power can continue until the incoming line is withdrawn. Furthermore, based on the allowable power change rate of the energy storage unit, it can be verified whether the energy storage unit can reach and stably maintain the corresponding energy storage support power before the expected operating time of the bus tie switch 7.

[0083] In some implementations, the power transfer coefficient on the support side and the power transfer coefficient on the compensation side are determined based on the equivalent impedance of the two transformers. The power transfer coefficient represents the change in active power of the bus tie after the bus tie switch 7 is closed when the corresponding energy storage unit generates a unit power change.

[0084] The equivalent impedance of the first transformer 1 and the second transformer 2 can be the positive sequence equivalent impedance referred to the same bus voltage level. When the voltage ratio, connection group, voltage regulation tap and secondary voltage of the two transformers are matched, and the impedance angle of the equivalent impedance of the two transformers is close, the power sharing factor can be approximately determined based on the magnitude of the equivalent impedance.

[0085] Let the equivalent impedances of the first transformer 1 and the second transformer 2 be denoted as Z1 and Z2, respectively. Then the power sharing coefficients of the first transformer 1 and the second transformer 2 can be expressed as follows:

[0086] β1 = |Z2| / (|Z1| + |Z2|);

[0087] β2 = |Z1| / (|Z1| + |Z2|).

[0088] After the bus tie switch 7 is closed, the predicted active power of the incoming lines of the first transformer 1 and the second transformer 2 can be expressed as follows:

[0089] PT1*=β1(PN1+PN2;

[0090] PT2*=β2(PN1+PN2)

[0091] When the direction of active power flow from the first busbar 5 to the second busbar 6 is taken as the positive direction of the bus coupler active power, the predicted active power of the bus coupler can be expressed as:

[0092] PM* = PT1* - PN1;

[0093] Or it can be expressed as:

[0094] PM* = PN2 - PT2*.

[0095] Under the simplified conditions described above, the coefficient of change in active power of the bus tie caused by the increase in unit discharge power of the first energy storage unit 12 is positive, and its magnitude can be approximated as β2; the coefficient of change in active power of the bus tie caused by the increase in unit discharge power of the second energy storage unit 13 is negative, and its magnitude can be approximated as β1. Therefore, when the first energy storage unit 12 is a support-side energy storage unit, its support-side power transfer coefficient can be determined as positive β2; when the second energy storage unit 13 is a support-side energy storage unit, its support-side power transfer coefficient can be determined as negative β1. The compensation-side power transfer coefficient is determined accordingly based on the bus where the compensation-side energy storage unit is located.

[0096] For systems where the impedance angles of the two transformers' equivalent impedances differ significantly, or where the tap positions and secondary voltages of the two transformers differ, an AC power flow model can be established that includes the equivalent impedances of the two transformers, the equivalent secondary power supply, and the net injected power of the two bus sections. Keeping other power parameters constant, a preset unit power perturbation is applied to an energy storage unit, and the power transfer coefficient of the corresponding energy storage unit is determined based on the ratio of the difference in predicted active power before and after the perturbation to the unit power perturbation. The unit power perturbation can be selected as one to five percent of the rated power of the energy storage unit to balance computational resolution and local linear approximation accuracy.

[0097] Based on the correspondence between the busbar where the supporting energy storage unit is located and the incoming and retained incoming lines, as well as the energy storage support direction and the positive direction of the bus coupler active power, the sign of the supporting side power transfer coefficient is determined. Based on the sign of the predicted active power of the busbar where the compensation side energy storage unit is located and the bus coupler support, the compensation power direction that can reduce the absolute value of the predicted active power of the bus coupler is selected.

[0098] Let ΔPESs be the change in energy storage support power in the included direction, and Ks be the power transfer coefficient on the support side. Then, the change in active power of the bus coupler caused by the energy storage support power can be expressed as:

[0099] ΔPMs = Ks × ΔPESs.

[0100] The predicted active power supported by the bus tie can be expressed as:

[0101] PMsup = PM0 + ΔPMs.

[0102] Let ΔPESc be the actual change in charging and discharging power of the compensation-side energy storage unit, and Kc be the power transfer coefficient of the compensation side. Then, the change in active power of the bus tie caused by the compensation-side energy storage unit can be expressed as:

[0103] ΔPMc = Kc × ΔPESc.

[0104] The predicted active power of the bus tie compensation can be expressed as:

[0105] PMcomp = PMsup + ΔPMc.

[0106] Based on PM0, PMsup, and PMcomp, the supporting power exposure, pre-compensation demand, and effective compensation power can be determined respectively. For operating ranges where the power flow model exhibits significant nonlinearity, the power flow calculation can be recalculated using the latest transferred power data after each stage of power regulation is completed by the compensation-side energy storage unit, instead of continuing to use the initial power transfer coefficient for linear extrapolation.

[0107] In some implementations, controlling the adjustment of the actual charging and discharging power of the compensation-side energy storage unit includes determining the target power change, determining the power regulation margin, limiting the target power change and the power change rate, and performing power regulation in stages.

[0108] When the absolute value of the power transfer coefficient Kc on the compensation side is greater than the preset minimum transfer coefficient, the target power change of the energy storage unit on the compensation side can be determined according to the following formula:

[0109] ΔPESc,target=-sgn(PMsup)×Ppre / Kc;

[0110] Where ΔPESc,target represents the target power change of the energy storage unit on the compensation side, and sgn is the sign function. When the target power change is positive, it indicates an increase in discharge power or a decrease in charging power compared to before the adjustment; when the target power change is negative, it indicates an increase in charging power or a decrease in discharge power.

[0111] When the absolute value of the power transfer coefficient on the compensation side is not greater than the preset minimum transfer coefficient, it indicates that the power change of the energy storage unit on the compensation side is insufficient to form sufficient bus power compensation. At this time, the target power change is not calculated further, the current automatic power transfer process is stopped, and the information of insufficient power transfer capacity on the compensation side is output.

[0112] When the bus tie switch 7 remains open, increasing the discharge power of the energy storage unit on the compensation side will reduce the active power of the transformer connected to the same bus, while increasing the charging power will increase the active power of the transformer's incoming line. The energy management controller determines whether the active power of the transformer's incoming line will approach the upper or lower boundary of the allowable power range based on the charging or discharging direction corresponding to the target power change, and determines the power regulation margin based on the difference between the current active power and the corresponding allowable power range boundary.

[0113] The energy management controller also limits the target power change and power change rate based on the maximum allowable charging power, maximum allowable discharging power, current actual charging and discharging power, current state of charge, minimum allowable state of charge, maximum allowable state of charge, remaining energy, and allowable power change rate of the compensation-side energy storage unit. When the maximum effective compensation power that can be formed after being limited by the above conditions is still less than the pre-compensation requirement, the bus joint control signal is not sent, and the insufficient compensation capacity is output.

[0114] When the compensation capacity meets the requirements, the limited target power change is divided into multiple power regulation levels. Each power regulation level can be 10% to 25% of the target power change, or it can be adaptively determined based on the power regulation margin of the compensation-side transformer. The energy management controller sends graded power regulation commands sequentially according to the limited power change rate, and obtains the actual charging and discharging power of the compensation-side energy storage unit after each power regulation command is issued.

[0115] When the direction of change of the actual charging and discharging power is consistent with the direction of the compensation power, and the effective compensation power calculated based on the actual charging and discharging power reaches the compensation power required by the current level power adjustment command within a consecutive preset number of sampling periods, the power adjustment of that level is confirmed to be complete, and then the next level power adjustment command is sent. For example, the sampling period can be set to one second, and the number of consecutive confirmations can be set to three. The above values ​​are only one implementation method and can be adjusted according to the response speed of the energy storage converter and the degree of power fluctuation on site.

[0116] In some implementations, in addition to ensuring that the effective compensation power and the active power of the incoming line of the compensation-side transformer meet the requirements, the closing control signal sent to the bus tie switch 7 should also meet the conditions of switch status, protection status, synchronization status and data timeliness.

[0117] The switch status conditions include that both the first incoming switch 14 and the second incoming switch 15 are in the closed position, and the bus tie switch 7 is in the open position. The protection status conditions include that no protection action signal or closing lockout signal is detected acting on the first incoming switch 14, the second incoming switch 15, or the bus tie switch 7.

[0118] Synchronization conditions include that the phase sequence on both sides of bus tie switch 7 is the same, and the voltage amplitude difference, frequency difference, and phase angle difference on both sides of bus tie switch 7 do not exceed the corresponding preset thresholds. For example, the voltage amplitude difference threshold can be set to 5% of the rated voltage, the frequency difference threshold can be set to 0.2Hz, and the phase angle difference threshold can be set to 10°. The specific thresholds can be determined according to the operating requirements of bus tie switch 7, the two transformers, and the upstream power grid.

[0119] The data timeliness conditions include the acquisition time of the actual energy storage power data used to determine the effective compensation power, the active power data of the incoming lines of the two transformers, and the voltage data on both sides of the bus tie switch 7. The time interval between these acquisition times and the current closing determination time shall not exceed the corresponding preset effective time limit. The effective compensation power should also be maintained for a preset number of sampling cycles until the pre-compensation requirement is met.

[0120] In some implementations, the active power of the incoming lines of the two transformers during the short-term parallel power supply phase can be predicted based on the current power transfer data before the busbar closing, and it can be determined whether the predicted active power of the two transformers is within the corresponding short-term parallel operation allowable power range. When either predicted active power exceeds the corresponding short-term parallel operation allowable power range, the closing control signal is not sent temporarily.

[0121] Before the bus tie switch 7 is actually connected, if any closing condition is no longer met, the energy management controller will stop outputting the closing control signal and output a closing lockout signal to the bus tie switch 7. After obtaining valid data again and confirming that all conditions have been restored, the closing determination process can be restarted.

[0122] In some implementations, determining whether the two busbars are actually connected includes acquiring the closed auxiliary contact signal of the bus tie switch 7, and acquiring at least one of the current flowing through the bus tie switch 7 and the equivalent impedance at both ends of the bus tie switch 7.

[0123] When the closing auxiliary contact signal is continuously maintained for a preset confirmation time, and the current flowing through the bus tie switch 7 is greater than the connection current threshold, it is determined that the main circuit of the bus tie switch 7 is conducting. When the power of the two bus sections is close to balanced, so that the actual current after the bus tie is closed is insufficient to reach the connection current threshold, the equivalent impedance at both ends of the break can be determined according to the voltage and current detection devices installed on both sides of the bus tie switch 7, and the two bus sections are actually connected when the equivalent impedance does not exceed the preset conduction impedance threshold.

[0124] The preset confirmation time can be determined based on the mechanical action time of the bus tie switch 7 and the anti-jitter time of the auxiliary contacts. When a closing auxiliary contact signal is received, but neither the required bus tie current nor the required equivalent impedance of the break point is detected within the preset confirmation time, it is determined that the bus tie switch 7 has a closing abnormality. At this time, a tripping control signal is sent to the bus tie switch 7 to stop the adjustment of the support-side energy storage unit in the direction of increasing energy storage support power, and to control the compensation-side energy storage unit to gradually restore to the actual charging and discharging power before the start of power adjustment.

[0125] In some implementations, when determining whether two busbars are actually connected, the time of determination is defined as the actual connection time. The energy storage support power actually provided by the support-side energy storage unit, the effective compensation power generated by the compensation-side energy storage unit, and the actual active power flowing through the bus tie switch 7 are recorded at this time. The energy storage support power actually provided by the support-side energy storage unit at the actual connection time is defined as the support power reference, and the effective compensation power at the actual connection time is defined as the compensation power reference.

[0126] The difference between the bus tie active power limit and the absolute value of the actual active power of the bus tie at the actual connection time is determined as the bus tie residual power margin. When the actual connection time is used as the reference for parallel power supply control, the bus tie residual power margin is also called the reference power margin.

[0127] The current supported power coverage can be determined by the following formula:

[0128] Pcover=max(0,M0+Peff,cur-Peff,base);

[0129] Where Pcover is the current supported power coverage, M0 is the remaining power margin of the bus tie at the actual connection time, i.e., the reference power margin, Peff,cur is the current effective compensation power, and Peff,base is the compensation power reference. When the current effective compensation power is lower than the compensation power reference, Peff,cur-Peff,base is a negative value, and the supported power coverage is reduced accordingly.

[0130] When the active power of the incoming line of the support-side transformer approaches the boundary of the corresponding allowable power range, and an increase in energy storage support power is required, the increase in energy storage support power is denoted as ΔPadd. Based on the power transfer coefficient of the support side and the current actual active power of the bus tie, the predicted active power of the bus tie before and after increasing the energy storage support power is determined respectively. The increase in bus tie power can be expressed as:

[0131] Pinc=max(0,|PM,after|-|PM,before|);

[0132] Wherein, PM,before represents the predicted active power of the bus tie before the increase of energy storage support power, and PM,after represents the predicted active power of the bus tie after the increase of energy storage support power.

[0133] When Pinc does not exceed Pcover, the supporting energy storage units are allowed to increase their energy storage supporting power according to the corresponding power change rate. When Pinc exceeds Pcover, the compensation-side energy storage units are first controlled to continue increasing their effective compensation power. Only when the actual increase in effective compensation power relative to the compensation power reference reaches the difference between Pinc and the supporting power coverage determined before adjusting the compensation-side energy storage units, are the supporting energy storage units allowed to increase their energy storage supporting power.

[0134] During the parallel power supply of two transformers, the actual energy storage support power provided by the supporting side energy storage unit shall not be lower than the support power benchmark recorded at the actual connection time, and the absolute value of the actual active power of the bus tie shall not exceed the active power limit of the bus tie. When the compensation side energy storage unit is unable to generate the required new effective compensation power due to limitations of state of charge, power limit, or fault state, the current actual charging and discharging power of the supporting side energy storage unit shall remain unchanged, the outgoing line withdrawal process shall be suspended, and abnormal information of the transfer process shall be output.

[0135] In some implementations, controlling the exit of the incoming line to be withdrawn includes pre-exit prediction, tripping execution, exit confirmation, and post-exit power restoration.

[0136] Based on the current power transfer data, the energy management controller sets the predicted active power of the transformer corresponding to the incoming line to be decommissioned to zero. It then determines the predicted active power that the transformer connected to the retained incoming line needs to handle, as well as the predicted active power flowing through bus tie switch 7, based on the power flow topology after the incoming line is decommissioned. The prediction process can also consider line losses, transformer losses, and the margin for changes in photovoltaic power and load power from the current time to the expected decommissioning time.

[0137] When the predicted active power of the retained-side transformer is within the corresponding allowable power range, and the absolute value of the predicted active power of the bus tie does not exceed the bus tie active power limit, a tripping control signal is sent to the incoming switch corresponding to the incoming line to be withdrawn. When the retained-side transformer or bus tie switch 7 does not meet the above conditions, the actual charging and discharging power of the two energy storage units continues to be adjusted, or the withdrawal process is suspended and the information of insufficient carrying capacity on the retained side is output.

[0138] After sending the trip control signal, the system determines whether the incoming line to be withdrawn has been withdrawn based on the auxiliary contact signal of the corresponding incoming line switch and the incoming current of the incoming line. When the auxiliary contact signal is continuously held for a preset confirmation time and the incoming current of the incoming line to be withdrawn is lower than the withdrawal current threshold, it is determined that the incoming line to be withdrawn has been withdrawn.

[0139] After the incoming line is withdrawn, the charging and discharging targets of the two energy storage units are redefined based on the actual active power of the retained transformer, the actual active power of the bus tie, the current photovoltaic power and load power of the two bus sections, and the current state of charge of the two energy storage units. The supporting and compensating power of the two energy storage units during the power transfer period is not simultaneously removed; instead, they gradually approach the redefined charging and discharging targets according to a preset power change rate. After each adjustment, the actual active power of the retained transformer and bus tie switch 7 is re-checked until the two energy storage units reach their respective redefined charging and discharging targets.

[0140] If the incoming line to be withdrawn is not determined to have exited within the preset withdrawal time limit after the tripping control signal is sent, the support power coverage continues to be determined according to the current effective compensation power and the remaining power margin of the bus tie. This limits the actual charging and discharging power changes of the energy storage units on the support side in the direction of increasing energy storage support power, and controls the energy storage units on the compensation side to adjust their actual charging and discharging power so that the absolute value of the actual active power flowing through the bus tie switch 7 remains within the bus tie active power limit. Simultaneously, an abnormal tripping signal for the incoming line to be withdrawn is output to facilitate on-site handling by operating personnel.

[0141] The above method is illustrated below with a set of operational data. This embodiment is only used to illustrate the calculation and control relationship between various power values; the actual power values ​​and limits can be determined based on the capacity and operational requirements of the photovoltaic energy storage system.

[0142] During periods of high photovoltaic output, the second incoming line is designated as a line to be decommissioned, while the first incoming line is reserved. The load power of the first busbar 5 is 800kW, the photovoltaic power is 2000kW, and the non-supporting reference power of the first energy storage unit 12 is 0kW; the load power of the second busbar 6 is 500kW, the photovoltaic power is 1100kW, and the non-supporting reference power of the second energy storage unit 13 is 0kW.

[0143] The permissible power range for the separate operation of the first transformer 1 is -1600kW to 2000kW, and the permissible power range for the separate operation of the second transformer 2 is -300kW to 1000kW. Based on the short-term parallel operation capability of the two transformers, the permissible power range for the short-term parallel operation of the first transformer 1 is -1600kW to 2200kW, and the permissible power range for the short-term parallel operation of the second transformer 2 within the preset parallel power supply time limit is -800kW to 1200kW.

[0144] If the second energy storage unit 13 recovers to its non-supported reference power, the net power consumption of the second bus 6 will be:

[0145] 500-1100-0=-600kW.

[0146] The active power of the incoming line of the second transformer 2 will reach -600kW, which is lower than the lower boundary of its permissible power range of split operation, -300kW. Therefore, the second energy storage unit 13 needs to maintain a charging power of 300kW. According to the rule that energy storage discharge is positive and charging is negative, the energy storage support direction of the second energy storage unit 13 is the charging direction, the energy storage support power Psup is 300kW, and the energy storage support power change ΔPESs including the direction is -300kW. The net power consumption of the second bus 6 becomes accordingly:

[0147] 500 - 1100 - (-300) = -300kW.

[0148] If the sum of the expected operating time of the bus tie switch 7, the parallel power supply time of the two transformers, and the preset exit time of the second incoming line is 90 seconds, then the second energy storage unit 13 needs to absorb approximately 7.5 kWh of electricity during this period. The second energy storage unit 13 can currently continue to be charged with 120 kWh of electricity, and the allowed charging power is 500 kW, thus enabling it to continuously provide the aforementioned energy storage support power for the expected power transfer duration.

[0149] The equivalent impedances of the two transformers are close at the current voltage regulation level, and the power sharing factor for both transformer 1 and transformer 2 is taken as 0.5. Without considering the 300kW charging support power of the second energy storage unit 13, the net power consumption of the first busbar 5 is -1200kW, the net power consumption of the second busbar 6 is -600kW, and the total predicted incoming active power after the two transformers are connected in parallel is -1800kW. The predicted incoming active power of the first transformer 1 is -900kW, and the bus tie baseline predicted active power is:

[0150] PM0 = -900 - (-1200) = 300kW.

[0151] Maintaining the 300kW charging support power of the second energy storage unit 13, the net power consumption of the second busbar 6 becomes -300kW, and the total predicted incoming active power of the two transformers becomes -1500kW. The predicted incoming active power of the first transformer 1 is -750kW, and the predicted active power supported by the bus tie is:

[0152] PMsup=-750-(-1200)=450kW.

[0153] Therefore, the supporting power exposure is:

[0154] Pexp = 450 - 300 = 150 kW.

[0155] Assuming the active power limit of the bus coupler is 400kW, the pre-compensation requirement is:

[0156] Ppre=450-400=50kW.

[0157] The first energy storage unit 12 is a compensation-side energy storage unit with a compensation-side power transfer coefficient of 0.5. In order to reduce the predicted active power of the bus tie support in the positive direction by 50kW, the first energy storage unit 12 needs to increase its charging power by 100kW.

[0158] With the bus tie switch 7 remaining open, the energy management controller progressively controls the first energy storage unit 12 to increase its charging power. When the actual charging / discharging power of the first energy storage unit 12 changes from 0kW to -104kW, based on its compensation-side power transfer coefficient of 0.5, it is determined that this actual power change will reduce the predicted active power of the bus tie by 52kW. At this time, the predicted active power of the bus tie compensation is:

[0159] PMcomp = 450 - 52 = 398 kW.

[0160] The effective compensation power is 52kW, which has already met the pre-compensation requirement of 50kW. The active power of the incoming line of the first transformer 1 before the bus tie switch 7 is closed is approximately:

[0161] 800-2000-(-104)=-1096kW,

[0162] The active power of the incoming line is within the allowable power range for the split operation of the first transformer 1.

[0163] Under the predicted state after the bus tie switch 7 is closed, the net power consumption of the first bus 5 is -1096kW, the net power consumption of the second bus 6 is -300kW, and the total predicted incoming active power of the two transformers is -1396kW. Based on a power sharing factor of 0.5, the predicted incoming active power of both the first transformer 1 and the second transformer 2 is approximately -698kW, which falls within the corresponding short-term parallel operation allowable power range.

[0164] When the first incoming line switch 14 and the second incoming line switch 15 are both in the closed position, the bus tie switch 7 is in the open position, no protection action signal or closing lockout signal is detected, the phase sequence, voltage amplitude difference, frequency difference and phase angle difference on both sides of the bus tie switch 7 meet the synchronization conditions, and the effective compensation power reaches the pre-compensation requirement for three consecutive sampling cycles, the energy management controller sends a closing control signal to the bus tie switch 7.

[0165] After bus tie switch 7 closes, its closed auxiliary contact signal remains continuously for a preset confirmation time, and electrical continuity is detected at both ends of bus tie switch 7. This corresponding moment is then determined as the actual connection moment. Assuming the active power of the bus tie detected at the actual connection moment is 396kW, the remaining power margin of the bus tie, i.e., the baseline power margin, is:

[0166] 400-396=4kW.

[0167] During parallel power supply, if the active power of the incoming line of the second transformer 2 changes, requiring the second energy storage unit 13 to increase its charging support power by 40kW, based on the power transfer coefficient on the support side of the second energy storage unit 13, it is predicted that this change in support power will increase the absolute value of the bus tie active power by 20kW. Since 20kW is greater than the reference power margin of 4kW, the energy management controller does not immediately increase the charging support power of the second energy storage unit 13, but instead controls the first energy storage unit 12 to further increase its charging power.

[0168] When the actual charging and discharging power of the first energy storage unit 12 is gradually adjusted from -104kW to -164kW, the charging power of the first energy storage unit 12 increases by 60kW relative to the actual connection time. Based on a compensation-side power transfer coefficient of 0.5, the actual effective increase in compensation power is 30kW, and the corresponding supported power coverage reaches:

[0169] 4 + 30 = 34kW.

[0170] Since the increase in bus power caused by the additional 40kW charging support power is 20kW, and the support power coverage does not exceed 34kW, the second energy storage unit 13 is allowed to adjust the actual charging and discharging power from -300kW to -340kW.

[0171] After the above adjustments are completed, the net power consumption of the first busbar 5 is:

[0172] 800-2000-(-164)=-1036kW;

[0173] The net power consumption of the second busbar 6 is:

[0174] 500-1100-(-340)=-260kW.

[0175] The energy management controller predicts the power flow after the second incoming line is disconnected based on the latest power transfer data. After the second incoming line is disconnected, the first transformer 1 will handle the total net power consumption of the two bus sections, and its predicted active power is:

[0176] -1036 + (-260) = -1296kW.

[0177] The net power consumption of the second busbar 6 is -260kW, therefore the predicted active power of the bus tie is -260kW, indicating that the second busbar 6 transmits 260kW of active power to the first busbar 5 via the bus tie switch 7. The predicted active power of the first transformer 1 is within its allowable power range, and the absolute value of the predicted active power of the bus tie, 260kW, is less than the bus tie active power limit of 400kW, therefore a trip control signal is sent to the second incoming switch 15.

[0178] When the auxiliary contact signal of the second incoming line switch 15 is detected, and the incoming current of the second incoming line is lower than the exit current threshold, it is determined that the second incoming line has exited. Subsequently, the charging and discharging targets of the first energy storage unit 12 and the second energy storage unit 13 are redefined based on the actual active power of the first transformer 1 and the bus tie switch 7. The two energy storage units are then controlled to gradually exit the pre-compensation state and support state during the power transfer period according to the preset power change rate, until the two energy storage units reach their respective redefined charging and discharging targets, thereby completing this live power transfer.

[0179] The embodiments described above are merely examples of several implementations of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A method for coordinated charging and discharging scheduling of a photovoltaic energy storage system, characterized in that, The photovoltaic energy storage system includes a first transformer and a second transformer that supply power to a first busbar and a second busbar respectively via a first incoming line and a second incoming line. The first busbar and the second busbar are connected by a bus tie switch, and each of the two busbar sections is connected to a photovoltaic branch, a load branch, and an energy storage unit; the method includes: In response to the request for live power transfer when the first transformer and the second transformer are operating separately, the incoming line to be withdrawn and the reserved incoming line are determined from the first incoming line and the second incoming line, and the active power of the incoming lines of the two transformers, the photovoltaic power and load power of the two bus sections, and the actual charging and discharging power of the two energy storage units are obtained. The obtained power data are determined as the power transfer data. Based on the relationship between the active power of the incoming lines and the allowable power range of the two transformers, the energy storage support power that needs to be maintained during the live power transfer period from the closing of the bus tie switch to the withdrawal of the incoming line is determined. The energy storage unit that provides the energy storage support power is determined as the support side energy storage unit, and the other energy storage unit is determined as the compensation side energy storage unit. Based on the busbar where the supporting energy storage unit is located, the incoming line to be withdrawn and the retained incoming line, the equivalent impedance of the two transformers, and the power transfer data, determine the amount of supporting power exposure that maintains the energy storage supporting power relative to the increase in the absolute value of the bus coupler active power caused by the closing of the bus coupler switch, and determine the pre-compensation requirement that ensures the absolute value of the predicted active power of the bus coupler does not exceed the bus coupler active power limit when maintaining the energy storage supporting power. With the bus tie switch kept open, the compensation-side energy storage unit is controlled to adjust the actual charging and discharging power, and the effective compensation power that can reduce the absolute value of the bus tie active power after the bus tie switch is closed is determined based on the change in the actual charging and discharging power of the compensation-side energy storage unit relative to the amount of change in the actual charging and discharging power before the power adjustment begins. When the effective compensation power reaches the pre-compensation requirement, and the active power of the incoming line of the transformer connected to the same bus as the compensation-side energy storage unit is within the corresponding allowable power range, a closing control signal is sent to the bus tie switch.

2. The charging and discharging coordinated scheduling method for a photovoltaic energy storage system according to claim 1, characterized in that, Determining the supporting power exposure, pre-compensation requirement, and effective compensation power includes: Based on the correspondence between the incoming line to be withdrawn and the retained incoming line and the two busbars, the equivalent impedance of the two transformers and the power transfer data, the bus coupler reference predicted active power is determined when the energy storage support power is not considered and the bus coupler support predicted active power is determined when the energy storage support power is maintained. When the absolute value of the predicted active power of the bus coupler support is greater than the absolute value of the predicted active power of the bus coupler reference, the difference between the two absolute values ​​is determined as the support power exposure; when the absolute value of the predicted active power of the bus coupler support is not greater than the absolute value of the predicted active power of the bus coupler reference, the support power exposure is determined to be zero. When the absolute value of the predicted active power supported by the bus tie is greater than the bus tie active power limit, the amount of reduction in bus tie active power required to reduce the absolute value of the predicted active power supported by the bus tie to no more than the bus tie active power limit is determined as the pre-compensation requirement; when the absolute value of the predicted active power supported by the bus tie is not greater than the bus tie active power limit, the pre-compensation requirement is determined to be zero. The actual charge and discharge power change of the compensation-side energy storage unit relative to the power adjustment before the start is obtained, and the bus tie compensation predicted active power when the compensation-side energy storage unit generates the actual charge and discharge power change is determined based on the actual charge and discharge power change, its corresponding charging or discharging direction, and the equivalent impedance of the two transformers. When the absolute value of the predicted active power of the bus tie compensation is less than the absolute value of the predicted active power of the bus tie support, the difference between the two absolute values ​​is determined as the effective compensation power; when the absolute value of the predicted active power of the bus tie compensation is not less than the absolute value of the predicted active power of the bus tie support, the effective compensation power is determined to be zero.

3. The charging and discharging coordinated scheduling method for a photovoltaic energy storage system according to claim 1, characterized in that, The first and second incoming lines are respectively equipped with a first incoming line switch and a second incoming line switch; after sending a closing control signal to the bus tie switch, the system further includes: The closed position of the bus tie switch and the electrical continuity detection result characterizing whether the two ends of the bus tie switch are connected are obtained, and the actual connection of the two bus sections is determined based on the closed position and the electrical continuity detection result. When it is determined that the two busbars are actually connected, the actual charging and discharging power, effective compensation power and actual active power flowing through the bus tie switch of the support side energy storage unit at the actual connection time are recorded, and the remaining power margin of the bus tie at the actual connection time is determined according to the actual active power and the bus tie active power limit. During the parallel power supply of the incoming line to be decommissioned and the reserved incoming line, the active power of the incoming lines of the two transformers, the photovoltaic power and load power of the two bus sections, and the actual charging and discharging power of the two energy storage units are continuously acquired. The newly acquired power data are determined as the current power transfer data. The current effective compensation power is updated according to the change in the actual charging and discharging power of the compensation-side energy storage unit relative to the power adjustment before it started. The support power coverage is determined according to the increase in the current effective compensation power relative to the actual connection time and the remaining power margin of the bus tie. The support-side energy storage unit is controlled so that the absolute increase in the active power of the bus tie caused by the change in the actual charging and discharging power relative to the actual connection time does not exceed the support power coverage. Based on the current power transfer data, the predicted power flow after the incoming line to be withdrawn is determined, and based on the predicted power flow, the predicted active power of the transformer connected to the retained incoming line and the predicted active power flowing through the bus tie switch are determined. When the predicted active power of the incoming line is within the allowable power range of the transformer connected to the retained incoming line, and the absolute value of the predicted active power does not exceed the bus tie active power limit, a trip control signal is sent to the incoming switch corresponding to the incoming line to be withdrawn. If, after sending the closing control signal, it is not determined that the two busbars are actually connected within a preset time limit, the adjustment of the actual charging and discharging power of the support-side energy storage unit in the direction of increasing the energy storage support power is stopped, and the compensation-side energy storage unit is controlled to restore to the actual charging and discharging power before the start of the power adjustment.

4. The charging and discharging coordinated scheduling method for a photovoltaic energy storage system according to claim 1, characterized in that, Determining the energy storage support power includes: The actual charging and discharging power of the two energy storage units was obtained when the preset support reference conditions were met most recently before the power transfer request was generated. The preset support reference conditions include that the active power of the transformer connected to the same bus with each energy storage unit is within the corresponding allowable power range, and the energy storage unit has not yet adjusted its charging and discharging power according to the active power of the incoming line. The two actual charging and discharging powers obtained were determined as the non-support reference power of the corresponding energy storage unit. Based on the current active power of the two transformers, the current actual charging and discharging power of the corresponding energy storage unit and the non-support reference power, determine the predicted active power of the two transformers when the corresponding energy storage unit recovers to the non-support reference power. When the predicted active power of the incoming line of a transformer is outside the allowable power range of that transformer when the support is removed, and the predicted active power of the incoming line of another transformer is within the allowable power range of that other transformer, the former is identified as the target transformer. Based on the difference between the predicted active power of the incoming line of the target transformer after support removal and the boundary of the allowable power range adjacent to the predicted active power of the incoming line after support removal, the energy storage support power required to keep the active power of the incoming line of the target transformer within the allowable power range is determined. The expected power transfer duration is determined based on the preset operating time limit, preset parallel power supply time limit, and preset exit time limit of the incoming line to be withdrawn from the bus tie switch. The required power supply is then determined based on the expected power transfer duration and the energy storage support power. The sustainable execution capability of the energy storage support power is verified based on the available power, allowable charging and discharging power, and current actual charging and discharging power of the energy storage unit corresponding to the target transformer. When the available power is not less than the power required for support, and the energy storage support power is within the allowable charging and discharging power range of the energy storage unit corresponding to the target transformer, it is determined that the energy storage support power can continue until the incoming line to be withdrawn is withdrawn, and the energy storage unit corresponding to the target transformer is determined as the support-side energy storage unit.

5. The charging and discharging coordinated scheduling method for a photovoltaic energy storage system according to claim 2, characterized in that, The direction of active power flowing from the first busbar to the second busbar via the bus tie switch is defined as the positive direction of bus tie active power, and the direction of power discharge from the energy storage unit to its busbar is defined as the positive direction of energy storage active power. The power transfer coefficient on the support side and the power transfer coefficient on the compensation side are determined based on the equivalent impedance of the two transformers. The power transfer coefficient on the support side characterizes the change in active power of the bus tie caused by the unit power change of the energy storage unit on the support side after the bus tie switch is closed. The power transfer coefficient on the compensation side characterizes the change in active power of the bus tie caused by the unit power change of the energy storage unit on the compensation side after the bus tie switch is closed. Based on the correspondence between the busbar where the supporting energy storage unit is located and the incoming line to be withdrawn and the retained incoming line, as well as the positive direction of the active power of the bus coupler, the sign of the supporting power transfer coefficient is determined, and the direction of the compensation power that can offset the supporting power exposure is determined based on the busbar where the compensation energy storage unit is located. Based on the photovoltaic power, load power and actual charging and discharging power of the corresponding energy storage units of the two bus sections, the net injected power of the two bus sections is determined respectively, and the bus tie reference predicted active power is determined based on the net injected power and the equivalent impedance of the two transformers. The change in busbar active power caused by the energy storage support power is determined based on the energy storage support power and the support-side power transfer coefficient. The busbar support predicted active power is determined based on the change in busbar active power and the busbar reference predicted active power. The support power exposure is determined based on the increase in the absolute value of the busbar support predicted active power relative to the absolute value of the busbar reference predicted active power. The change in active power of the bus tie on the compensation side is determined based on the actual charge and discharge power change of the energy storage unit on the compensation side and the power transfer coefficient on the compensation side. The predicted active power of the bus tie is determined based on the change in active power of the bus tie on the compensation side and the predicted active power of the bus tie support. The effective compensation power is determined based on the decrease in the absolute value of the predicted active power of the bus tie support relative to the absolute value of the predicted active power of the bus tie compensation.

6. The charging and discharging coordinated scheduling method for a photovoltaic energy storage system according to claim 5, characterized in that, Controlling the compensation-side energy storage unit to adjust the actual charging and discharging power includes: The target power change of the compensation-side energy storage unit is determined based on the pre-compensation demand and the compensation-side power transfer coefficient. Based on the direction of the compensation power that can reduce the absolute value of the predicted active power of the bus coupler support, the compensation-side energy storage unit is determined to perform charging regulation or discharging regulation. Based on the charging or discharging direction corresponding to the target power change, determine the boundary of the allowable power range that the active power of the transformer connected to the same busbar as the compensation-side energy storage unit will approach, and determine the power adjustment margin based on the difference between the active power of the incoming line and the boundary of the allowable power range. Based on the power regulation margin, the allowable charging and discharging power range of the compensation-side energy storage unit, and the remaining power, the target power change amount and power change rate are limited; According to the limited power change rate, a graded power adjustment command is sent to the compensation-side energy storage unit, and the actual charging and discharging power of the compensation-side energy storage unit is obtained after each power adjustment command is issued. When the direction of change of the actual charging and discharging power is consistent with the direction of the compensation power, and the effective compensation power determined based on the actual charging and discharging power reaches the compensation power required by the corresponding graded power adjustment command within a consecutive preset number of sampling periods, the power adjustment of that grade is confirmed to be complete.

7. The charging and discharging coordinated scheduling method for a photovoltaic energy storage system according to claim 3, characterized in that, Sending a closing control signal to the bus tie switch also satisfies the following conditions: The first and second incoming line switches are both in the closed position, the bus tie switch is in the open position, and no protection action signal or closing lockout signal is detected acting on the first incoming line switch, the second incoming line switch or the bus tie switch; The phase sequence on both sides of the bus tie switch is the same, and the voltage amplitude difference, frequency difference and phase angle difference on both sides of the bus tie switch do not exceed the corresponding preset thresholds. The time interval between the acquisition time of each data point used to determine the effective compensation power, the active power of the two transformer incoming lines, and the voltage on both sides of the bus tie switch and the current closing determination time shall not exceed the corresponding preset effective time limit. The effective compensation power reaches the pre-compensation requirement and is continuously maintained for a preset number of sampling periods. Specifically, before the bus tie switch is actually connected, if any of the aforementioned conditions are no longer met, the closing control signal is stopped from being output, and a closing lockout signal is output to the bus tie switch.

8. The charging and discharging coordinated scheduling method for a photovoltaic energy storage system according to claim 3, characterized in that, Determining whether two busbar segments are actually connected includes: Obtain the closed auxiliary contact signal of the bus tie switch, and obtain at least one of the current flowing through the bus tie switch and the equivalent impedance at both ends of the bus tie switch break. When the closing auxiliary contact signal is continuously maintained for a preset confirmation time, and the current flowing through the bus tie switch is greater than the connection current threshold or the equivalent impedance at both ends of the bus tie switch does not exceed the preset conduction impedance threshold, it is determined that the two bus sections are actually connected. When the closing auxiliary contact signal is received but no electrical connection condition is met within a preset confirmation time, it is determined that the bus tie switch has a closing abnormality. A trip control signal is sent to the bus tie switch to stop adjusting the actual charging and discharging power of the support-side energy storage unit in the direction of increasing the energy storage support power, and the compensation-side energy storage unit is controlled to restore to the actual charging and discharging power before the power adjustment started.

9. The charging and discharging coordinated scheduling method for a photovoltaic energy storage system according to claim 5, characterized in that, After sending a closing control signal to the bus tie switch, the closed position status of the bus tie switch and the electrical connection detection result characterizing whether the two ends of the bus tie switch are connected are obtained. When it is determined that the two bus sections are actually connected, the energy storage support power, effective compensation power and actual active power flowing through the bus tie switch actually provided by the support side energy storage unit are recorded at the actual connection time. The actual energy storage support power provided by the support-side energy storage unit at the actual connection time is determined as the support power benchmark, the effective compensation power at the actual connection time is determined as the compensation power benchmark, and the difference between the bus tie active power limit and the absolute value of the actual active power flowing through the bus tie switch at the actual connection time is determined as the benchmark power margin. The actual charging and discharging power of the compensation-side energy storage unit is continuously acquired, and the current effective compensation power is updated according to the change in the actual charging and discharging power of the compensation-side energy storage unit relative to the amount of actual charging and discharging power before the power adjustment begins. When it is determined that the energy storage support power needs to be increased based on the active power of the incoming line of the transformer connected to the same busbar as the support-side energy storage unit, the predicted active power of the busbar before and after increasing the energy storage support power is determined based on the energy storage support power to be increased, the power transfer coefficient of the support side, and the actual active power flowing through the bus tie switch. When the absolute value of the predicted active power of the bus after increasing the energy storage support power is greater than the absolute value of the predicted active power of the bus before increasing the energy storage support power, the difference between the two absolute values ​​is determined as the increase in bus power; when the absolute value of the predicted active power of the bus after increasing the energy storage support power is not greater than the absolute value of the predicted active power of the bus before increasing the energy storage support power, the increase in bus power is determined to be zero. The support power coverage is determined based on the increase in current effective compensation power relative to the compensation power reference and the reference power margin; When the increase in bus power does not exceed the support power coverage, the support-side energy storage unit is allowed to adjust its actual charging and discharging power in the direction of increasing the energy storage support power; when the increase in bus power exceeds the support power coverage, the compensation-side energy storage unit is first controlled to increase its effective compensation power, and after the actual increase in effective compensation power relative to the compensation power reference reaches the difference between the increase in bus power and the support power coverage determined before adjusting the compensation-side energy storage unit, the support-side energy storage unit is allowed to adjust its actual charging and discharging power in the direction of increasing the energy storage support power. During the period when the two transformers are supplying power in parallel, the actual energy storage support power provided by the support-side energy storage unit is not less than the support power benchmark, and the absolute value of the actual active power flowing through the bus tie switch does not exceed the bus tie active power limit.

10. The charging and discharging coordinated scheduling method for a photovoltaic energy storage system according to claim 3, characterized in that, Controlling the exit of the incoming line to be retracted includes: Based on the current power transfer data, determine the predicted active power of the transformer connected to the retained incoming line after the incoming line to be withdrawn, as well as the predicted active power flowing through the bus tie switch. When the predicted active power of the incoming line is within the allowable power range of the transformer connected to the reserved incoming line, and the absolute value of the predicted active power does not exceed the bus tie active power limit, a trip control signal is sent to the incoming line switch corresponding to the incoming line to be deactivated. When it is determined that the incoming line to be withdrawn has been withdrawn based on the position status of the incoming line switch corresponding to the incoming line to be withdrawn and the incoming line current of the incoming line to be withdrawn, the charging and discharging targets of the two energy storage units are redefined based on the active power of the transformer connected to the retained incoming line after withdrawal and the actual active power flowing through the bus tie switch. The actual charging and discharging power of the two energy storage units is controlled to gradually approach their respective redefined charging and discharging targets until the corresponding charging and discharging targets are reached. If the incoming line to be withdrawn is not determined to be withdrawn within the preset time limit after the tripping control signal is sent, the support power coverage continues to be determined based on the current effective compensation power and the remaining power margin of the bus tie, limiting the actual charging and discharging power change generated by the support-side energy storage unit in the direction of increasing the energy storage support power, and controlling the compensation-side energy storage unit to adjust the actual charging and discharging power so that the absolute value of the actual active power flowing through the bus tie switch does not exceed the bus tie active power limit, and outputting an abnormal tripping signal for the incoming line to be withdrawn.

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