Multi-port DAB energy storage system directly connected with elevator frequency converter bus and cooperative control method of multi-port DAB energy storage system

Abstract

The invention discloses a multi-port DAB energy storage system directly connected with an elevator frequency converter bus and a cooperative control method of the multi-port DAB energy storage system, and is suitable for an elevator frequency converter direct-current bus direct-connection scene. Aiming at the defects in the aspects of elevator bus transient support, multi-branch extension and parallel operation safety access in the prior art, at least two DAB power branches are adopted, the low-voltage sides of the DAB power branches are connected into the same low-voltage direct-current source in parallel to realize current expansion, and the high-voltage sides of the DAB power branches are connected to a VFD direct-current bus through a parallel operation access switch to realize voltage expansion after being connected in series and laminated; the controller adopts fixed frequency phase shift control, and combines a two-line parallel operation or power-off time sequence and a zero-crossing residence strategy; through multi-branch phase interleaving, mutual exclusion amplitude limiting constraint, ZVS guarantee and a fault striding linkage mechanism, branch power balance, circulating current suppression and bus stable support are realized. According to the invention, the millisecond voltage of the bus can be efficiently suppressed, the response speed, the operation efficiency and the reliability of the system are improved, and the core requirements of elevator bus energy recovery and transient stability control are met.

Description

Technical Field

[0001] This invention relates to the fields of power electronics and elevator energy-saving storage technology, specifically to a multi-port DAB energy storage system directly connected to the elevator inverter bus and its collaborative control method. Background Technology

[0002] During elevator operation, the DC bus of the frequency converter frequently undergoes energy feedback and absorption during regenerative braking and traction acceleration phases, resulting in large bus voltage amplitude, rapid ascent / descent speeds, and frequent power direction switching. To address the energy and voltage stability issues during this process, traditional solutions primarily employ braking resistors to consume regenerative energy or energy feedback units to feed energy back to the grid. However, braking resistors suffer from energy waste and significant heat generation, while energy feedback units face drawbacks such as high cost and limited grid adaptability.

[0003] In recent years, technical solutions have emerged that directly connect energy storage units to the elevator DC bus to achieve energy recovery and transient bus support. However, existing technologies still have significant drawbacks in practical applications: The transient response requirements of the bus are stringent: the millisecond-level voltage spikes and drops of the elevator bus require the converter to have the ability to quickly adjust bidirectionally at a fixed frequency, and to achieve low-impact and controllable switching when the power direction crosses zero. Existing solutions are difficult to meet this transient performance requirement. Resonant converters have poor adaptability: Resonant schemes, represented by LLC, usually rely on frequency conversion control or mode switching when performing bidirectional power transmission and wide-range power adjustment, resulting in lagging control response, poor parallel consistency, and inability to meet the transient support of elevator bus, rapid zero-crossing switching and multi-branch expansion requirements. The parallel connection of multiple branches is complex: In engineering scenarios where parallel connection is achieved through only two DC cables, the pre-charging, excitation, contactor closing and control loop closing processes are coupled with each other, which can easily generate surge current, excitation impact and metering deviation, seriously affecting the system's operational stability and acceptance consistency. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-port DAB energy storage system and its collaborative control method directly connected to the elevator inverter bus, aiming to solve the technical pain points in existing elevator bus direct-connected energy storage solutions.

[0005] This invention is implemented as follows: a multi-port DAB energy storage system directly connected to the elevator inverter bus, comprising: Elevator inverter DC bus; A low-voltage DC power supply is used to connect the battery and energy storage unit; At least two DAB power branches, where n≥2, each of the DAB power branches includes a low-voltage full bridge, a high-voltage full bridge, an isolation transformer and a series inductor, the isolation transformer realizes electrical isolation between the low-voltage side and the high-voltage side, and the high-voltage side DC output terminal of each branch forms an electrically independent high-voltage side DC link. Parallel connection switches and controllers, including pre-charge contactors and main contactors; The low-voltage side inputs of each DAB power branch are connected in parallel to the low-voltage DC source, and the high-voltage side DC outputs of each DAB power branch are connected in series to form a superimposed voltage link. The two ends of the superimposed voltage link are connected to the positive and negative terminals of the DC bus of the elevator inverter through the parallel access switch to realize parallel access. The controller is used to adjust the phase shift angle between the low-voltage full bridge and its corresponding high-voltage full bridge of each DAB power branch at a fixed switching frequency, so as to realize bidirectional power exchange between the low-voltage DC source and the DC bus of the elevator inverter; the controller is also used to allocate power to the total power command based on the capacity parameters of each branch, and apply phase interleaving and mutual exclusion limiting constraints to suppress circulating current, and to perform voltage equalization control or voltage equalization protection based on the voltage sampling value of the high-voltage side of each branch in the high-voltage side series superimposed link and trigger the orderly exit of the branch.

[0006] Preferably, the additional inductance portion of the series inductor accounts for 60%-80% of the total equivalent inductance, and a minimum commutation current threshold is set to ensure ZVS.

[0007] Preferably, the branch phase interleaving angle is 60°-120°, and a mutual exclusion limiting constraint is applied: when n=2, |φ1|+|φ2|≤φ_sum,max is satisfied; when n>2, Σ|φi|≤φ_sum,max is satisfied, or a similar constraint is applied to any two branches to suppress the circulation. The value of φ_sum,max is 0.2π-0.6π, and the minimum phase shift is determined by the ZVS criterion.

[0008] Preferably, in the high-voltage side series superimposed link, a voltage sampling module is set at the high-voltage output terminal of each branch to collect the high-voltage side voltage sampling value. The voltage sampling module adopts the method of isolation amplifier, isolation ADC or differential sampling and isolation digital transmission. The high-voltage side full bridge drive and sampling circuit of each branch has isolated power supply isolation measures.

[0009] Preferably, the system further includes redundant branches. When an abnormality of overcurrent, overvoltage, or overtemperature is detected in a branch, the abnormal branch is shut down and isolated according to the phase-shifting zero-return and symmetrical demagnetization strategy; the remaining branches maintain derating operation or are taken over by the redundant branches. The high-voltage and low-voltage side devices are Si and SiC MOSFETs or IGBTs; the transformer is a single transformer with multiple windings or multiple independent transformers; the parallel connection switch uses mechanical contactors, solid-state relays or hybrid switches; the controller is an MCU, DSP and FPGA.

[0010] This invention also discloses a collaborative control method for a multi-port DAB energy storage system directly connected to the elevator inverter bus, characterized by comprising: (1) Generate a total power command with the DC bus voltage of the elevator inverter as the main control quantity; allocate the total power command according to the capacity constraints of each branch to obtain the power command of each branch; (2) Calculate the phase shift angle for each branch at a fixed switching frequency, and apply phase interleaving and mutual exclusion limiting constraints to the phase shift angle; (3) Set minimum phase shift clamping and power limiting strategies based on ZVS criterion; (4) When a branch fault or an abnormality of the DC bus of the elevator inverter or a power grid drop is detected, the phase shift angle of the abnormal branch is rapidly approached to 0 and symmetrical demagnetization is performed before orderly shutdown. At the same time, other branches are controlled to enter the bus support and absorption mode to maintain bus stability, and after the abnormality is restored, the power is smoothly returned to the target power by ramp.

[0011] Preferably, the capacity constraints of each branch include at least one of the following: energy storage-side SOC, temperature, current limiting, and lifetime model.

[0012] Preferably, the mutual exclusion limiting constraint is: when n=2, |φ1|+|φ2|≤φ_sum,max; when n>2, Σ|φi|≤φ_sum,max, or a similar constraint is applied to any two branches.

[0013] Preferably, the ZVS criterion is determined based on a commutation current threshold or capacitance / dead time. The branch faults include overcurrent, overvoltage, and overtemperature faults.

[0014] Preferably, in the light load or small phase shift range, the system enters the minimum circulating current or intermittent modulation mode to balance ZVS and efficiency.

[0015] Compared with the prior art, the beneficial effects of the present invention are: Excellent transient response performance: The DAB topology with fixed frequency phase shift control naturally supports bidirectional energy flow and fast power adjustment, which can be adapted to the scenario of frequent switching of elevator bus regeneration and traction, and achieve millisecond-level voltage spike and drop suppression and controllable zero-crossing switching, solving the response lag problem of traditional solutions; High flexibility for expansion: The structural design of parallel current amplification on the low-voltage side and series voltage amplification on the high-voltage side allows each branch to bear only part of the voltage and current stress. The system power and voltage level can be flexibly expanded according to the number of branches, and it supports N+1 redundancy configuration, improving engineering applicability. Good safety and consistency in parallel operation: The power-on or power-off sequence of the two-line parallel operation decouples the pre-charging, magnetization, closing, loop closing and demagnetization processes, effectively reducing surge current, excitation impact and metering deviation, and improving the stability and acceptance consistency of parallel operation. High operating efficiency and reliability: Phase interleaving and mutual exclusion limiting constraints reduce the risk of synthetic ripple and circulating current. Combined with ZVS criterion and minimum phase shift clamping, device stress is reduced and conversion efficiency is improved. Branch fault exit and straddle linkage mechanism can avoid fault propagation, reduce the impact of single branch faults or power grid drops on elevator operation, and significantly improve system reliability. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the system framework of the present invention; Figure 2 This is a schematic diagram of the dual transformer DAB power stage structure of the present invention; Figure 3 This is a flowchart of the power-on or power-off timing of the two-wire parallel operation of the present invention; Figure 4 This is a collaborative control block diagram of the present invention; Figure 5 This is a schematic diagram of fault handling and power grid drop-through of the present invention; Detailed Implementation

[0017] 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.

[0018] The following description, in conjunction with the accompanying drawings and specific embodiments, provides further details: Example 1 like Figure 1As shown, the system includes an elevator inverter DC bus, a low-voltage DC source, and multiple branch DAB power stages connected in parallel with the bus. The low-voltage side inputs of multiple DAB power branches (140-1…140-n) are connected in parallel to the same low-voltage DC source. The high-voltage side DC outputs of each branch are connected in series and superimposed to form the equivalent output on the bus side. Its two ends are connected to the positive and negative terminals of the DC bus through parallel access switches such as Kpre / Kmain, thereby realizing parallel access.

[0019] The high-voltage side power stage consists of a high-voltage side full-bridge assembly (120-1…120-n) and at least two branches. Taking a dual-transformer model as an example, it can be expanded to have n branches. The DAB power stage is as follows: Figure 2 ; like Figure 2 As shown, each DAB power branch achieves bidirectional power transmission at a fixed frequency through phase shifting between the low-voltage full bridge and the high-voltage full bridge. Figure 2 For simplification, the high-voltage side full bridge is not shown for ease of explanation. Its output is connected to the high-voltage winding of the corresponding isolation transformer and then fed into the high-voltage side series superimposed voltage link. The series inductor can be placed on the low-voltage side or the high-voltage side, or combined with the transformer leakage inductance to form an equivalent inductance, used to limit commutation current and facilitate ZVS (Zero Voltage Spectrometry). Optionally, each branch is configured with current detection and current sharing / limiting logic to suppress circulating and bias currents caused by parameter differences.

[0020] Feasibility requirements for series voltage stacking: To achieve series voltage stacking on the high-voltage side and adapt to different common-mode potentials in each branch, it is preferable to form electrically independent DC links at the high-voltage side DC output terminals of each branch, including high-voltage side DC link capacitors and necessary filtering / discharge channels; and to sample the voltage Vhv_i at the high-voltage side DC output terminal of each branch using an isolation / differential method, so that voltages of each segment can still be obtained and voltage equalization control and protection determination can be performed under series voltage stacking. The high-voltage side full-bridge drive and sampling circuits of each branch preferably have isolated power supply or equivalent isolation measures to ensure reliable control and measurement of each branch and no interference during series voltage stacking.

[0021] Series voltage equalization and protection: To ensure consistent voltage distribution across all branches of the series voltage equalization link on the high-voltage side, it is preferable to set voltage sampling at the DC output terminal of the high-voltage side of each branch and incorporate it into power distribution / phase shift compensation to achieve active voltage equalization; or configure a passive voltage equalization network / bypass channel to limit imbalance. When Vhv_i of any branch exceeds the threshold or an abnormal circulating current is detected, the controller performs power limiting, adjusts power distribution, or triggers the orderly exit of that branch to maintain the safety of the series link.

[0022] like Figure 3As shown, by cooperating with Kpre, Kmain, and the controller, low-surge parallel operation is achieved in a scenario where only two DC cables are connected to the bus. For ease of description, the total voltage of the superimposed link is defined as Vstack = ΣVhv_i, where Vhv_i is the sampled voltage value of the DC output terminal of the high-voltage side of the i-th branch.

[0023] The power-on phase includes: (1) Precharge: Keep the main contactor Kmain open, close the precharge branch Kpre, so that the superimposed link and the bus can be slowly charged / discharged through the precharge channel to limit the surge current; the controller continuously monitors Vbus and Vstack, and monitors the voltage window and imbalance of each segment Vhv_i.

[0024] (2) Magnetization and soft loop closing: When Kmain is still disconnected, the controller applies a small phase shift φ_pre to each branch to establish transformer excitation and realize slow energy exchange through the Kpre channel, so that Vstack approaches Vbus. At the same time, it performs active voltage equalization or voltage equalization protection according to Vhv_i.

[0025] (3) Closing conditions: When |Vstack−Vbus|≤ΔV_on and all branch Vhv_i are within the allowable window and the imbalance is ≤ΔV_bal, the main contactor Kmain is closed; then closed-loop control is entered.

[0026] (4) Ramp connection: After the Kmain is closed, the controller smoothly switches from small phase shift to power / bus voltage closed loop, and the phase shift angle climbs to the target value according to the preset ramp to avoid contactor closing transient impact.

[0027] Zero crossing stage: When the power direction crosses zero and the phase shift angle is close to 0, the controller stays in the range of |φ|≤φ_hold for a preset PWM period and limits the phase shift change rate dφ / dt to suppress di / dt, reduce metering deviation and improve the consistency of multiple branches.

[0028] Power-down phase: The controller first returns the phase shift angle to zero by ramping, and after executing the symmetrical demagnetization preset cycle, disconnects the main contactor Kmain; then disconnects the precharge branch Kpre and completes the safe power-down, thereby achieving low-impact, low-surge power-on or power-off switching.

[0029] like Figure 4 As shown, the controller includes a bus voltage loop, a power divider, a phase shift scheduler, and a protection module. The power divider generates and distributes branch power commands based on energy storage-side SOC / temperature / current limiting / lifetime models, etc.; the phase shift scheduler outputs the phase shift angle of each branch at a fixed frequency and applies phase interleaving and mutual exclusion limiting constraints; the protection module sets φ_min and power limiting strategies based on the ZVS criterion, and triggers branch exit / shutdown and system-level straddle linkage when fault conditions are met.

[0030] like Figure 5 As shown, when an abnormality such as overcurrent / overvoltage / overtemperature is detected in a certain branch, the phase shift of that branch quickly approaches 0 and performs symmetrical demagnetization before orderly shutdown; other branches enter bus support or absorption mode to reduce the impact of bus fluctuations on elevator operation. During power grid dips or abnormal bus voltage, the system can implement power limiting and straddle strategies, and smoothly exit with a ramp after recovery.

[0031] The following is a two-branch (n=2) DAB energy storage system with the following specific configuration: The low-voltage DC power supply uses a lithium battery pack with a rated voltage of 200V; The low-voltage sides of the two DAB power branches are connected in parallel to the lithium battery pack, and the high-voltage side DC output is connected in series and then connected to the elevator VFD DC bus with a rated voltage of 750V through Kpre and Kmain. The isolation transformer ratio of each branch is set to 1:2.5, and the series inductor adopts a combination of external inductor and transformer leakage inductance, with the external inductor accounting for 70% of the total equivalent inductance; The controller uses a DSP chip, the switching frequency is set to 60kHz, the branch phase interleaving angle is 90°, the mutual exclusion limiting constraint is set to |φ1|+|φ2|≤0.4π, and the minimum phase shift φ_min is determined to be 0.05π by the ZVS criterion; Power-on phase: Pre-charge time is set to 3s, ΔV_on=10V, ΔV_bal=5V, phase shift angle climbs to the target value within 0.5s in an S-shaped ramp; zero-crossing dwell for 1 PWM cycle; power-off phase symmetrical demagnetization for 2 cycles; Working process: During elevator regenerative braking, the bus energy is transferred to the lithium battery pack for storage through the high-voltage full bridge, isolation transformer, series inductor and low-voltage full bridge; during elevator traction acceleration, the lithium battery pack energy is transferred back to the bus to provide transient support; the controller achieves power equalization by adjusting the phase shift angle of the two branches, and performs active voltage equalization based on the sampled values ​​of Vhv_1 and Vhv_2 to suppress circulating current.

[0032] N-branch extension system (n=4): When higher power is required, such as a rated power of 60kW or a higher bus voltage, four DAB power branches are used for extension, as detailed below: The low-voltage side is still connected in parallel to the same 200V lithium battery pack, and the high-voltage side has 4 branches connected in series and stacked to adapt to the 1000V bus. The branch phase interleaving angle is set to 60° (360° / 4), and the mutual exclusion amplitude limiting constraint is set to Σ|φi|≤0.5π; Power distribution strategy: The controller dynamically distributes power commands based on the temperature data collected by the temperature sensors of each branch and the estimated SOC value. Branches with excessively high temperature or excessively high / low SOC are appropriately derated to ensure balanced operation of the branches. Extended advantages: Each branch only needs to withstand 250V high voltage and 15kW power, reducing the difficulty and cost of component selection. In addition, if any branch fails, the other three branches can maintain 45kW power output to ensure the basic operation of the elevator.

[0033] N+1 Redundancy System: Based on the above 4 branches, add 1 redundant branch (n=5) to form an N+1 redundancy system. The redundant branch has the same hardware configuration as the other four working branches, and normally operates under low load, allocating 10% of the total power. When an overcurrent (threshold 20A), overvoltage, high-voltage side voltage exceeding 270V, or overtemperature (IGBT temperature exceeding 85℃) is detected in a working branch, the controller immediately returns the phase angle of that branch to zero, performs two cycles of symmetrical demagnetization, and then shuts it off. At the same time, the redundant branch quickly takes over the power distribution of the faulty branch, increasing it from 10% to 30%, while the remaining three working branches maintain their original power distribution to ensure stable total power output of the system. The branch is equipped with a bypass switch. After the faulty branch is shut down, the bypass switch closes to maintain the continuity of the series link on the high-voltage side and avoid system shutdown caused by the disconnection of the series link.

[0034] 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 multi-port DAB energy storage system directly connected to the busbar of an elevator frequency converter, characterized in that, include: Elevator inverter DC bus; A low-voltage DC power supply is used to connect the battery and energy storage unit; At least two DAB power branches, where n≥2, each of the DAB power branches includes a low-voltage full bridge, a high-voltage full bridge, an isolation transformer and a series inductor, the isolation transformer realizes electrical isolation between the low-voltage side and the high-voltage side, and the high-voltage side DC output terminal of each branch forms an electrically independent high-voltage side DC link. Parallel connection switches and controllers, including pre-charge contactors and main contactors; The low-voltage side inputs of each DAB power branch are connected in parallel to the low-voltage DC source, and the high-voltage side DC outputs of each DAB power branch are connected in series to form a superimposed voltage link. The two ends of the superimposed voltage link are connected to the positive and negative terminals of the DC bus of the elevator inverter through the parallel access switch to realize parallel access. The controller is used to adjust the phase shift angle between the low-voltage full bridge and its corresponding high-voltage full bridge of each DAB power branch at a fixed switching frequency, so as to realize bidirectional power exchange between the low-voltage DC source and the DC bus of the elevator inverter; the controller is also used to allocate power to the total power command based on the capacity parameters of each branch, and apply phase interleaving and mutual exclusion limiting constraints to suppress circulating current, and to perform voltage equalization control or voltage equalization protection based on the voltage sampling value of the high-voltage side of each branch in the high-voltage side series superimposed link and trigger the orderly exit of the branch.

2. The multi-port DAB energy storage system directly connected to the elevator inverter bus as described in claim 1, characterized in that, The added portion of the series inductor accounts for 60%-80% of the total equivalent inductance, and a minimum commutation current threshold is set to ensure ZVS.

3. The multi-port DAB energy storage system directly connected to the elevator inverter bus as described in claim 1, characterized in that, The branch phase interleaving angle is 60°-120°, and a mutual exclusion limiting constraint is applied: when n=2, |φ1|+|φ2|≤φ_sum,max is satisfied; when n>2, Σ|φi|≤φ_sum,max is satisfied, or a similar constraint is applied to any two branches to suppress the circulation. The value of φ_sum,max is 0.2π-0.6π, and the minimum phase shift is determined by the ZVS criterion.

4. The multi-port DAB energy storage system directly connected to the elevator inverter bus as described in claim 1, characterized in that, In the high-voltage side series superimposed link, a voltage sampling module is set at the high-voltage output terminal of each branch to collect the high-voltage side voltage sampling value. The voltage sampling module adopts the method of isolation amplifier, isolation ADC or differential sampling and isolation digital transmission. The high-voltage side full bridge drive and sampling circuit of each branch has isolated power supply isolation measures.

5. A multi-port DAB energy storage system directly connected to the elevator inverter bus as described in claim 1, characterized in that, The system also includes redundant branches. When an abnormality of overcurrent, overvoltage, or overtemperature is detected in a branch, the abnormal branch is turned off and isolated according to the phase-shifting zero-return and symmetrical demagnetization strategy. The remaining branches will continue to operate at reduced capacity or will be taken over by redundant branches; The high-voltage and low-voltage side devices are Si and SiC MOSFETs or IGBTs; the transformer is a single transformer with multiple windings or multiple independent transformers; the parallel connection switch uses mechanical contactors, solid-state relays or hybrid switches; the controller is an MCU, DSP and FPGA.

6. The collaborative control method for a multi-port DAB energy storage system directly connected to the elevator inverter bus as described in claim 1, characterized in that, include: (1) Generate a total power command with the DC bus voltage of the elevator inverter as the main control quantity; allocate the total power command according to the capacity constraints of each branch to obtain the power command of each branch; (2) Calculate the phase shift angle for each branch at a fixed switching frequency, and apply phase interleaving and mutual exclusion limiting constraints to the phase shift angle; (3) Set minimum phase shift clamping and power limiting strategies based on ZVS criterion; (4) When a branch fault or an abnormality of the DC bus of the elevator inverter or a power grid drop is detected, the phase shift angle of the abnormal branch is rapidly approached to 0 and symmetrical demagnetization is performed before orderly shutdown. At the same time, other branches are controlled to enter the bus support or absorption mode to maintain the stability of the bus. After the abnormality is restored, the power is smoothly returned to the target power by ramping.

7. The collaborative control method for a multi-port DAB energy storage system directly connected to an elevator frequency converter bus as described in claim 6, characterized in that, The capacity constraints of each branch include at least one of the following: energy storage-side SOC, temperature, current limiting, and lifetime model.

8. The collaborative control method for a multi-port DAB energy storage system directly connected to the elevator inverter bus as described in claim 6, characterized in that, The mutual exclusion limit constraint is as follows: when n=2, |φ1|+|φ2|≤φ_sum,max is satisfied; when n>2, Σ|φi|≤φ_sum,max is satisfied, or a similar constraint is applied to any two branches.

9. The collaborative control method for a multi-port DAB energy storage system directly connected to an elevator frequency converter bus as described in claim 6, characterized in that, The ZVS criterion is determined based on the commutation current threshold or capacitance and dead time. The branch faults include overcurrent, overvoltage, and overtemperature faults.

10. The collaborative control method for a multi-port DAB energy storage system directly connected to an elevator inverter bus as described in claim 6, characterized in that, In the light load or small phase shift range, the system enters the minimum circulating current or intermittent modulation mode to balance ZVS and efficiency.

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