A master-slave bidirectional current window control method and system for a one-and-two elevator energy storage system

Abstract

This invention discloses a master-slave bidirectional current window control method and system for elevator energy storage. The system includes a first bidirectional DC-DC unit, a second bidirectional DC-DC unit, and a shared energy storage unit, each connected to the DC bus of two elevators. The first bidirectional DC-DC unit acts as the master unit, defining the master current and slave current as current quantities with positive and negative directions, and using I_pack = I_A + I_B to determine the net current of the energy storage unit. The master unit generates a bidirectional window W_B = [I_B_min, I_B_max] for the slave unit based on its own current occupancy and the allowable charging and discharging boundaries of the energy storage unit. The slave unit generates its local demand current based on its own bus voltage, and after direction switching buffering, it limits the current within the window. This method limits the total charging and discharging current under the same-direction operating condition, and allows energy cancellation under the one-charge-one-discharge operating condition, so that the regenerated energy is preferentially consumed by the other elevator, while reducing the complexity of communication, algorithms, and on-site debugging.

Description

Technical Field

[0001] This invention relates to the field of industrial communication technology, specifically to a master-slave bidirectional current window control method and system for a one-to-two elevator energy storage system. Background Technology

[0002] During heavy-load descent, light-load ascent, and deceleration braking processes, the traction motor operates in regenerative power generation mode, which increases the DC bus voltage of the frequency converter. Traditional solutions use braking resistors to dissipate the regenerative energy as heat, which not only wastes energy but also leads to increased machine room temperature rise, accelerated aging of the braking resistors, and increased cooling load on the machine room air conditioning, resulting in high operating costs and low energy efficiency.

[0003] In a one-to-two elevator application scenario, the two elevators share a set of high-rate energy storage units, which can effectively reduce system costs and space occupation, and improve equipment integration. However, the operating status of the two elevators is random, and they may simultaneously generate electricity and consume traction power, or one may generate electricity and the other consume traction power. If the two bidirectional DC-DC converters are completely independently controlled without a coordination mechanism, the total charging and discharging current of the energy storage unit may exceed the safety boundary, leading to risks such as battery overcurrent, overcharging, and over-discharging. If a control architecture is adopted that centrally controls and distributes the target current of the two channels, there are drawbacks such as long control links, large communication delays, high algorithm complexity, high hardware costs, and difficult on-site debugging, which are not conducive to engineering implementation and mass application. Summary of the Invention

[0004] The purpose of this invention is to provide a master-slave bidirectional current window control method and system for a one-to-two elevator energy storage system, which aims to achieve the control effect of overcurrent prevention in the same direction and energy complementarity in the opposite direction, while simplifying the system architecture and reducing the difficulty of engineering implementation.

[0005] This invention is implemented as follows: a master-slave bidirectional current window control method for a one-to-two elevator energy storage system, comprising: The first bidirectional DC-DC unit and the second bidirectional DC-DC unit are respectively connected to the DC bus of the first elevator inverter and the DC bus of the second elevator inverter, and the first bidirectional DC-DC unit and the second bidirectional DC-DC unit are connected to the same energy storage unit. The first bidirectional DC-DC unit is configured as the master unit and the second bidirectional DC-DC unit is configured as the slave unit. The equivalent current I_A on the battery side of the master unit and the equivalent current I_B on the battery side of the slave unit are defined as current quantities with positive and negative directions, where a positive value indicates charging the energy storage unit and a negative value indicates discharging from the energy storage unit. The host obtains I_A and the maximum allowable charging current I_chg_max and the maximum allowable discharging current I_dis_max of the energy storage unit, and generates a bidirectional allowable current window W_B for the slave based on I_A, I_chg_max, I_dis_max and safety margin. The W_B includes the allowable discharge boundary I_B_min and the allowable charging boundary I_B_max. The host sends the bidirectional allowable current window W_B to the slave; The slave device generates a local demand current I_B_req based on its own DC bus voltage, and limits the local demand current I_B_req within W_B to obtain the final execution current I_B_ref; wherein, the master device does not directly specify the target current of the slave device, but issues a bidirectional current boundary to constrain the local demand current of the slave device.

[0006] Preferably, the net current I_pack of the energy storage unit satisfies I_pack = I_A + I_B; when I_A and I_B have the same sign, the net current is superimposed in the same direction, and when I_A and I_B have opposite signs, the net current is canceled out in opposite directions; the bidirectional allowable current window is generated according to the net current boundary, so that I_pack does not exceed the allowable charging boundary or allowable discharging boundary of the energy storage unit.

[0007] Preferably, the bidirectional current window is generated as follows: I_pack_min = -I_dis_max + I_margin, I_pack_max = I_chg_max - I_margin, I_B_min_raw = I_pack_min - I_A, I_B_max_raw = I_pack_max - I_A, where I_margin is a safety margin.

[0008] Preferably, the host further performs secondary limiting on I_B_min_raw and I_B_max_raw based on the slave's rated charging capacity, rated discharging capacity, temperature, SOC, BMS allowable state or fault derating state to obtain the final I_B_min and I_B_max.

[0009] Preferably, the slave device generates a positive local demand current when its DC bus voltage is higher than the charging threshold V_H, generates a negative local demand current when its DC bus voltage is lower than the discharging threshold V_L, and generates a zero current or standby command when its DC bus voltage is between V_L and V_H. When the master and slave are in the same direction of charging or discharging, the bidirectional current window limits the sum of the master current and slave current to not exceeding the allowable charging or discharging boundary of the energy storage unit.

[0010] Preferably, the final execution current I_B_ref is obtained through a clamping function: I_B_ref = clamp(I_B_req, I_B_min, I_B_max).

[0011] Preferably, the first bidirectional DC-DC unit and the second bidirectional DC-DC unit adopt DAB, non-isolated Buck-Boost, bidirectional LLC or other bidirectional power transfer conversion topologies.

[0012] Preferably, when the master and slave are in reverse charging and discharging conditions, the bidirectional allowable current window allows the slave to execute current in the opposite direction within the net current boundary, so that the regenerated energy recovered on one side is preferentially drawn and consumed by the other side, and only the difference is borne by the energy storage unit. The host sends the bidirectional current window, enable / disable information, communication sequence number and check field to the slave via RS-485, CAN, isolated UART or Ethernet. When the slave device does not receive a valid bidirectional current window, the slave device first maintains the previous valid window, then narrows the window periodically according to a preset ratio, and then enters the safety window. After the preset disconnection time is exceeded, charging and discharging are prohibited. When the slave device switches between charging and discharging states, it first reduces the current command to zero or near zero and holds it for a preset time before entering the new operating direction. The protection priority for local overcurrent, overvoltage, undervoltage, overtemperature, drive failure, or BMS disabled status of the slave device is higher than that of the bidirectional current window sent by the host.

[0013] Preferably, the energy storage unit is a lithium titanate battery, a supercapacitor, a lithium battery, a lithium-ion capacitor, or a hybrid energy storage unit.

[0014] The present invention also discloses a one-to-two elevator energy storage system, including a first elevator inverter DC bus, a second elevator inverter DC bus, a first bidirectional DC-DC unit, a second bidirectional DC-DC unit, an energy storage unit, and a communication bus; the first bidirectional DC-DC unit is configured as a master unit, the second bidirectional DC-DC unit is configured as a slave unit, and executes the control method described in any one of claims 1 to 14.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention provides accurate current judgment and more reasonable constraints: it adopts a unified definition of signed current and calculates the net current of the energy storage unit by algebraic sum, which accurately reflects the actual current stress borne by the battery, replacing the rough limitation of the traditional absolute value addition, and avoiding excessive current limiting under reverse operating conditions.

[0016] Improved energy efficiency and reduced battery loss: Under reverse operation, the two energy sources can directly complement each other, and the regenerated energy is preferentially consumed by the elevator on the opposite side, reducing the charging and discharging throughput and current stress of the energy storage unit, reducing battery heating, SOC fluctuation and cycle loss, and extending battery life.

[0017] Clear safety boundaries and high operational reliability: The bidirectional window simultaneously limits the bidirectional boundaries of slave charging and discharging, and combined with the hierarchical communication degradation mechanism and local priority protection strategy, it comprehensively covers risk scenarios such as overcurrent, overcharge, over-discharge, and communication anomalies.

[0018] Simple architecture and low engineering implementation cost: Adopting a master-slave architecture, the master only issues window boundaries rather than target currents, resulting in small communication data volume and low latency requirements; the slave retains complete local control capabilities without relying on real-time commands from the master, reducing algorithm complexity, hardware costs, and on-site debugging difficulty, making it suitable for batch engineering applications. Attached Figure Description

[0019] Figure 1 is a block diagram of the overall architecture of the master-slave bidirectional current window control system for energy storage of a one-to-two elevator according to the present invention. Figure 2 is a control flowchart of the host A generating a bidirectional current window for slave B according to the present invention; Figure 3 is a control flowchart of the local orientation determination and window limiting execution of the slave device B in this invention; Figure 4 is a schematic diagram of the net battery current constraint under the same and opposite operating conditions of the present invention. Figure 5 is a schematic diagram of the window convergence and security degradation strategy when communication is lost according to the present invention. Detailed Implementation

[0020] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0021] The following description, in conjunction with the accompanying drawings and specific embodiments, provides further details: This invention uses a signed current definition: positive current represents charging the energy storage unit, and negative current represents discharging from the energy storage unit. The net current of the host A, slave B, and energy storage unit are in the same signed coordinate system, and the actual net current borne by the battery is determined by I_pack = I_A + I_B.

[0022]

[0023] Core Formula

[0024] System Composition like Figure 1 As shown, the system components, from left to right according to energy flow and control flow, are as follows: ① Elevator A inverter DC bus, corresponding to Vbus_A and bidirectional energy flow of channel A; ② Bidirectional DC-DC A, corresponding to master A, responsible for sampling I_A, obtaining BMS boundaries, and calculating slave window W_B; ③ Shared energy storage unit, corresponding to lithium titanate battery + BMS, providing boundaries such as I_chg_max, I_dis_max, SOC, temperature, and prohibited charging / discharging, and bearing net current I_pack; ④ Bidirectional DC-DC B, corresponding to slave B, receiving W_B, generating I_B_req according to Vbus_B, and executing I_B_ref=clamp(I_B_req,I_B_min,I_B_max); ⑤ Elevator B inverter DC bus, corresponding to Vbus_B and B-channel local charging, discharging, or standby determination. The dashed communication link in the figure corresponds to the master-slave communication bus, used by the master to send W_B, enable, sequence number, and verification information.

[0025] Core technology solutions A master-slave control architecture The first bidirectional DC-DC unit is configured as master unit A, and the second bidirectional DC-DC unit is configured as slave unit B. Master unit A prioritizes responding to its own elevator's needs and periodically acquires its own signed battery-side current I_A.

[0026] Master A does not directly send the target current to the slave device; it only sends the bidirectional window W_B, enable / disable, sequence number, and verification information. Slave B retains local bus control and autonomously determines the direction and limits the execution based on its own bus voltage. Direction determination from the local bus of machine B

[0027] When V_H is greater than V_L, a hysteresis region is formed; this can be determined by combining filtering and duration to avoid frequent switching.

[0028] Based on the signed net current, a bidirectional window is generated for slave B. The host A obtains its own signed current I_A and converts the battery's allowable charge and discharge boundary into a bidirectional window W_B that can be used by the slave B.

[0029] I_pack_min = -I_dis_max + I_margin I_pack_max = I_chg_max - I_margin I_B_min_raw = I_pack_min - I_A I_B_max_raw = I_pack_max - I_A W_B = [I_B_min, I_B_max] The host can combine the slave's rated capacity, temperature, SOC, BMS permissible status and fault derating to perform secondary limiting on the original boundary.

[0030] Local demand limit execution from machine B Slave B generates its local demand current I_B_req based on its own bus status. This demand can be generated using a voltage loop, current loop, lookup table, or piecewise function. When switching charging / discharging directions, a slope limit or zero-current transition can be performed first; after receiving a valid window, the following steps are executed: I_B_ref = clamp(I_B_req, I_B_min, I_B_max) Therefore, B is responsible for determining whether to charge, discharge, or standby; the window provided by A only limits the available range of B and does not replace B's local bus control.

[0031] Unified handling of same-direction and opposite-direction working conditions

[0032] This method always uses the signed algebraic sum of I_pack = I_A + I_B as the constraint, instead of the rough constraint of adding the absolute values. This retains the energy cancellation capability of the reverse working condition and avoids unconstrained output from the slave.

[0033] Communication anomalies and local protection

[0034] Local protection takes precedence over host window and bus requirements, with the following preference order: Local Protection > Communication Validity > Host Window > Bus Requirements.

[0035] Control process Host A process 1. Collect the signed current I_A of channel A and determine the charging, discharging or standby needs of channel A.

[0036] 2. Obtain I_chg_max, I_dis_max, SOC, temperature, and BMS allow status.

[0037] 3. Calculate the net current boundary values ​​I_pack_min and I_pack_max.

[0038] 4. Calculate the original window values ​​I_B_min_raw and I_B_max_raw of slave B based on I_A.

[0039] 5. Generate the final window W_B by combining the slave's rated capacity and derating conditions.

[0040] 6. Periodically send W_B, enable / disable, sequence number, and checksum fields.

[0041] The window can be adjusted or the slave device can be disabled based on its status.

[0042] Slave B process 8. Acquire Vbus_B and perform filtering, hysteresis, and duration determination.

[0043] 9. Determine charging, discharging, or standby mode based on Vbus_B.

[0044] 10. Generate the local demand current I_B_req.

[0045] 11. When switching charging and discharging directions, first perform a direction switching buffer, and then process the transition according to the limited slope or zero current.

[0046] 12. Receive and verify W_B sent by host A.

[0047] 13. When the window is active, execute I_B_ref = clamp(I_B_req, I_B_min, I_B_max).

[0048] 14. When the window is invalid or communication is lost, enter the hold, convergence, safety window or disable output.

[0049] When local protection is triggered, protection will be executed first.

[0050] Typical Case Taking a one-to-two elevator energy storage system as an example, two bidirectional DC-DC units are connected to the DC buses of two elevators respectively and share the same energy storage unit. The first bidirectional DC-DC unit is the master unit A, and the second bidirectional DC-DC unit is the slave unit B. In this embodiment, the maximum charging and discharging current of the energy storage unit is 150A, and the maximum charging and discharging current of a single bidirectional DC-DC unit is also 150A. Considering the delays in sampling, communication, window updates, and current comparison between A and B, a safety margin of 10A is reserved, therefore the actual control boundary is calculated as 140A. Charging is defined as positive, and discharging as negative. I_pack = I_A + I_B.

[0051] Mode 1: A and B are charged simultaneously.

[0052] If A has been charged to 100A, then the window for B is: W_B = [-240A, +40A].

[0053] This means that B can only be charged at a maximum of 40A. If B requires charging at 80A, it will be limited to 40A to prevent the total charging current from exceeding 140A.

[0054] Mode 2: A charges, B discharges.

[0055] If A is charged at 100A, then the window for B is: W_B = [-240A, +40A].

[0056] According to the window control method, B can discharge up to 240A, but considering B's own discharge limit, the final discharge is 150A.

[0057] Mode 3: A and B discharge simultaneously.

[0058] If A has discharged 100A, then the window for B is: W_B = [-40A, +240A].

[0059] That is, B can only discharge a maximum of 40A. If B needs to discharge 80A, it is limited to 40A to prevent the total discharge current from exceeding 140A.

[0060] Mode 4: A discharges, B charges.

[0061] If A discharges 100A, then the window for B is: W_B = [-40A, +240A].

[0062] According to the window control method, B can charge up to 240A, but considering B's own charging limit, it will ultimately charge to 150A.

[0063] By using the above method, the total current is limited when working in the same direction, and positive and negative currents are allowed to cancel each other out when working in opposite directions, thereby reducing the actual current borne by the energy storage unit.

[0064] Key parameters and optional range

[0066] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A master-slave bidirectional current window control method for a one-to-two elevator energy storage system, characterized in that, include: The first bidirectional DC-DC unit and the second bidirectional DC-DC unit are respectively connected to the DC bus of the first elevator inverter and the DC bus of the second elevator inverter, and the first bidirectional DC-DC unit and the second bidirectional DC-DC unit are connected to the same energy storage unit. The first bidirectional DC-DC unit is configured as the master unit and the second bidirectional DC-DC unit is configured as the slave unit. The equivalent current I_A on the battery side of the master unit and the equivalent current I_B on the battery side of the slave unit are defined as current quantities with positive and negative directions, where a positive value indicates charging the energy storage unit and a negative value indicates discharging from the energy storage unit. The host obtains I_A and the maximum allowable charging current I_chg_max and the maximum allowable discharging current I_dis_max of the energy storage unit, and generates a bidirectional allowable current window W_B for the slave based on I_A, I_chg_max, I_dis_max and safety margin. The W_B includes the allowable discharge boundary I_B_min and the allowable charging boundary I_B_max. The host sends the bidirectional allowable current window W_B to the slave; The slave device generates a local demand current I_B_req based on its own DC bus voltage, and limits the local demand current I_B_req within W_B to obtain the final execution current I_B_ref; wherein, the master device does not directly specify the target current of the slave device, but issues a bidirectional current boundary to constrain the local demand current of the slave device.

2. The method according to claim 1, characterized in that, The net current I_pack of the energy storage unit satisfies I_pack = I_A + I_B; when I_A and I_B have the same sign, the net current is superimposed in the same direction, and when I_A and I_B have opposite signs, the net current is canceled out in opposite directions; the bidirectional allowable current window is generated according to the net current boundary, so that I_pack does not exceed the allowable charging boundary or allowable discharging boundary of the energy storage unit.

3. The method according to claim 1, characterized in that, The bidirectional current window is generated as follows: I_pack_min = -I_dis_max + I_margin, I_pack_max = I_chg_max - I_margin, I_B_min_raw = I_pack_min - I_A, I_B_max_raw = I_pack_max - I_A, where I_margin is a safety margin.

4. The method according to claim 3, characterized in that, The host further performs secondary limiting on I_B_min_raw and I_B_max_raw based on the slave's rated charging capacity, rated discharging capacity, temperature, SOC, BMS allowable state or fault derating state, to obtain the final I_B_min and I_B_max.

5. The method according to claim 1, characterized in that, The slave device generates a positive local demand current when its DC bus voltage is higher than the charging threshold V_H, generates a negative local demand current when its DC bus voltage is lower than the discharging threshold V_L, and generates a zero current or standby command when its DC bus voltage is between V_L and V_H. When the master and slave are in the same direction of charging or discharging, the bidirectional current window limits the sum of the master current and slave current to not exceeding the allowable charging or discharging boundary of the energy storage unit.

6. The method according to claim 1, characterized in that, The final execution current I_B_ref is obtained through a clamping function: I_B_ref = clamp(I_B_req, I_B_min, I_B_max).

7. The method according to claim 1, characterized in that, The first bidirectional DC-DC unit and the second bidirectional DC-DC unit adopt DAB, non-isolated Buck-Boost, bidirectional LLC or other bidirectional power transfer conversion topologies.

8. The method according to claim 1, characterized in that, When the master and slave are in reverse charging and discharging conditions, the bidirectional allowable current window allows the slave to execute current in the opposite direction within the net current boundary, so that the regenerated energy recovered on one side is preferentially drawn and consumed by the other side, and only the difference is borne by the energy storage unit. The host sends the bidirectional current window, enable / disable information, communication sequence number and check field to the slave via RS-485, CAN, isolated UART or Ethernet. When the slave device does not receive a valid bidirectional current window, the slave device first maintains the previous valid window, then narrows the window periodically according to a preset ratio, and then enters the safety window. After the preset disconnection time is exceeded, charging and discharging are prohibited. When the slave device switches between charging and discharging states, it first reduces the current command to zero or near zero and holds it for a preset time before entering the new operating direction. The protection priority for local overcurrent, overvoltage, undervoltage, overtemperature, drive failure, or BMS disabled status of the slave device is higher than that of the bidirectional current window sent by the host.

9. The method according to claim 1, characterized in that, The energy storage unit is a lithium titanate battery, a supercapacitor, a lithium battery, a lithium-ion capacitor, or a hybrid energy storage unit.

10. A one-to-two elevator energy storage system, characterized in that, It includes a first elevator inverter DC bus, a second elevator inverter DC bus, a first bidirectional DC-DC unit, a second bidirectional DC-DC unit, an energy storage unit, and a communication bus; the first bidirectional DC-DC unit is configured as a master unit, the second bidirectional DC-DC unit is configured as a slave unit, and executes the control method according to any one of claims 1 to 9.

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