Parallel control method and device for sodium salt energy storage system pcs

Abstract

The application discloses a sodium salt energy storage system PCS parallel control method and device, which is applied to a sodium salt energy storage system containing at least two PCSs; the control method comprises the following steps: being connected with a low-speed communication bus through a communication interaction circuit, synchronizing voltage frequency reference values of the PCSs, and acquiring system average current; generating an initial voltage reference instruction according to local output current and output voltage through a droop control circuit, and superimposing a virtual impedance compensation amount generated according to the output current in a droop control equation; fine-tuning the initial voltage reference instruction according to the deviation between local output current and system average current through a current sharing regulation circuit to generate a final voltage reference instruction; and communicating with a sodium salt battery management system through a sodium salt battery adaptation circuit, and adjusting a droop control coefficient according to received sodium salt battery state parameters.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, and in particular to a method and apparatus for parallel control of a sodium salt energy storage system PCS. Background Technology

[0002] Sodium-ion batteries have broad application prospects in large-scale energy storage power stations due to their abundant resources, low cost, and good safety. To meet the power requirements of energy storage units ranging from hundreds of kilowatts to megawatts, multiple PCS (Power Conversion Systems) are often operated in parallel. However, existing parallel control of multiple energy storage systems still faces many technical bottlenecks.

[0003] Due to the discreteness of hardware parameters of each PCS module and the asymmetry of line impedance, unwanted circulating currents will occur between parallel modules even when the same voltage command is given. Actual measurement data shows that circulating currents can reach 5% to 15% of the rated current, leading to increased current stress on switching devices and filters, reduced system efficiency, and in severe cases, even triggering false protection or equipment overload damage.

[0004] In terms of control strategies, existing solutions struggle to balance current sharing accuracy and dynamic response. While droop control can suppress circulating current by increasing the droop coefficient, it leads to severe voltage drops, poor current sharing accuracy, and slow dynamic response. Master-slave control, on the other hand, relies on microsecond-level high-speed communication, which carries the risk of single-point failure, high hardware costs, and weak anti-interference capabilities.

[0005] In terms of battery compatibility, existing PCS generally use the control logic of lithium-ion batteries, ignoring the unique characteristics of sodium-ion batteries, such as flat voltage plateau, temperature-sensitive internal resistance, and large performance differences at high and low temperatures. This results in severe loss of charge and discharge efficiency, shortened cycle life, and failure to fully utilize the performance advantages of sodium-ion batteries.

[0006] In addition, the existing solution has shortcomings in modularization and redundancy management. Faulty modules can only be replaced by system shutdown, expansion requires re-debugging, and lacks hot-swappable and dynamic reconfiguration capabilities, which seriously affects the maintainability and availability of the system.

[0007] Therefore, there is an urgent need for a low-cost, highly reliable, and efficient PCS parallel control device for sodium salt energy storage systems, which is particularly suitable for modular and scalable sodium salt energy storage container systems. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and device for parallel control of a sodium salt energy storage system PCS.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, the present invention provides a parallel control method for a sodium salt energy storage system PCS, applicable to a sodium salt energy storage system comprising at least two PCSs; the control method includes: connecting to a low-speed communication bus via a communication interaction circuit to synchronize the voltage frequency reference values ​​of each PCS and obtain the system average current; generating an initial voltage reference command based on the local output current and output voltage via a droop control circuit, and superimposing a virtual impedance compensation amount generated based on the output current into the droop control equation; fine-tuning the initial voltage reference command based on the deviation between the local output current and the system average current via a current sharing adjustment circuit to generate a final voltage reference command; and communicating with a sodium salt battery management system via a sodium salt battery adapter circuit to adjust the droop control coefficient based on the received sodium salt battery state parameters.

[0010] The control method further includes: calculating the circulating current amplitude in real time; when the circulating current amplitude exceeds the circulating current preset threshold, generating an incremental signal proportional to the difference between the circulating current amplitude and the circulating current preset threshold, and adjusting the virtual resistance value in the virtual impedance compensation amount in a stepwise manner; when the circulating current amplitude is lower than the circulating current preset threshold and a preset waiting time is continuously set, slowly returning the virtual resistance value to the initial value.

[0011] The incremental signal for the step-wise adjustment is calculated using the following formula.

[0012] in, For virtual resistance increment, The amplitude of the circulation. Preset threshold for circulation. The scaling factor is used; the step adjustment changes the virtual resistance value step by step at a first rate; the slow callback is performed at a second rate, and the second rate is less than the first rate.

[0013] The control method further includes temperature compensation, comprising: when the ambient temperature is lower than a preset low temperature threshold, increasing the base value of the virtual resistance value by a first preset ratio.

[0014] The communication cycle of the low-speed communication bus is 100ms; when communication is interrupted, the current sharing regulation circuit automatically degrades to independent droop control to achieve degraded operation.

[0015] The sodium-ion battery adapter circuit performs the following steps: adjusting the DC-side voltage operating point of the PCS according to a preset coefficient based on the total sodium-ion battery voltage; allocating the total power command of the parallel system proportionally according to the battery state of charge: in discharge mode, PCS with a higher state of charge is assigned a higher power weight; in charging mode, PCS with a lower state of charge is assigned a higher power weight; at the end of charging, when the total battery voltage exceeds the first charging threshold, it switches to constant voltage charging mode; when the total battery voltage exceeds the second charging threshold, it switches to trickle charging mode; when the total battery voltage exceeds the third charging threshold, it performs hard cutoff; at the end of discharging, when the total battery voltage is lower than the first discharging threshold, it initiates power decay; when the total battery voltage is lower than the second discharging threshold, it performs soft shutdown; when the total battery voltage is lower than the third discharging threshold, it performs hard cutoff; dynamically adjusting the power allocation weight according to the state of charge difference of each sodium-ion battery cluster, so that the state of charge difference between clusters converges to a preset target value.

[0016] The control method also includes redundancy management logic, which includes: broadcasting its own device number and health status through the low-speed communication bus, and dynamically electing a master coordinating PCS based on the health status and device number; triggering the reallocation of power commands when a PCS failure or new PCS is detected; and triggering a smooth switching process when a new PCS is detected.

[0017] The fault exit sequence includes: after fault detection, the faulty PCS controls the output power to be ramped to zero at a first preset rate; after the power is reduced to zero, the AC side circuit breaker is disconnected; at the same time, a fault offline message is broadcast through the low-speed communication bus; after the other PCS receives the fault offline message, it redistributes the power command according to the state of charge ratio. The smooth cut-in process includes: enabling the newly deployed PCS to detect the AC bus voltage and synchronize with the local output voltage until the amplitude difference is less than the first preset amplitude difference, the frequency difference is less than the first preset frequency difference, and the phase difference is less than the first preset phase difference; after synchronization is completed, enabling the newly deployed PCS to send a grid connection request through the low-speed communication bus; after receiving the redistributed power command, closing the AC side circuit breaker and controlling the output power to ramp up to the target value at a second preset rate.

[0018] On the other hand, the present invention provides a parallel control device for a sodium salt energy storage system PCS, applicable to a sodium salt energy storage system comprising at least two PCS, each PCS including a local controller, a sampling circuit, and a communication interface; the control device is integrated into the local controller and includes: A communication interaction circuit is connected to the communication interface and, through the communication interface, to a low-speed communication bus for synchronizing the voltage and frequency reference values ​​of each PCS and obtaining the system average current. A droop control circuit, connected to the sampling circuit, is used to generate an initial voltage reference command based on the output current and output voltage of the PCS; the droop control circuit integrates a virtual impedance compensation unit, which is used to generate a compensation amount based on the output current and superimpose it onto the droop control equation; The current sharing adjustment circuit is connected to the droop control circuit and the communication interaction circuit respectively, and is used to fine-tune the initial voltage reference command according to the deviation between the output current of the PCS and the average current of the system, and generate the final voltage reference command. The sodium salt battery adapter circuit is communicatively connected to the sodium salt battery management system and is used to adjust the droop control coefficient of the droop control circuit according to the received sodium salt battery status parameters.

[0019] In another aspect, the present invention provides a sodium salt energy storage system, comprising: multiple sodium salt battery clusters and corresponding sodium salt battery management systems; at least two PCS, each PCS including the aforementioned control device, and the DC side of each PCS being connected to the sodium salt battery clusters; a low-speed communication bus connecting all the PCS; and the AC sides of all PCS being connected in parallel to the same AC bus.

[0020] As can be seen from the above technical solutions, the advantages of the present invention are: By connecting the communication interaction circuit to a low-speed communication bus, distributed collaboration among PCSs is achieved, eliminating reliance on a single master controller and avoiding single-point-of-failure risks. By integrating a virtual impedance compensation unit into the droop control circuit, compensation amounts are generated based on the output current and superimposed on the droop control equation, actively compensating for output voltage deviations caused by hardware differences and effectively suppressing circulating current. The current sharing adjustment circuit fine-tunes the voltage reference command based on the deviation between the local output current and the system average current, achieving high-precision current sharing while reducing communication costs. Through a sodium-ion battery adaptation circuit communicating with the sodium-ion battery management system, the droop control coefficient is adjusted based on battery state parameters, achieving deep adaptation to the sodium-ion battery. Therefore, this invention provides a highly reliable, high-precision, and strongly adaptable parallel control device for PCS in a sodium-ion energy storage system.

[0021] Furthermore, this invention achieves adaptive adjustment of virtual impedance through circulating current detection and stepped adjustment; ensures stable operation under low-temperature conditions through temperature compensation; reduces communication costs and enhances robustness through low-speed communication and degraded operation; achieves full life cycle management of sodium-ion batteries through DC-side operating point adjustment, SOC power allocation, multi-level charge and discharge protection, and multi-cluster equalization; and improves system maintainability and availability by enabling hot-swappable modules and non-stop maintenance through dynamic election, uninterrupted exit, and smooth entry. Attached Figure Description

[0022] Figure 1A schematic diagram of the parallel control device for the sodium salt energy storage system PCS provided by the present invention; Figure 2 A flowchart of the parallel control method for a sodium salt energy storage system PCS provided by the present invention; Figure 3 for Figure 2 Flowchart of step S20; Figure 4 Another flowchart of the parallel control method for the sodium salt energy storage system PCS provided by the present invention; Figure 5 for Figure 4 Flowchart of step S50; Figure 6 A timing diagram of PCS failure exit and new PCS commissioning in the parallel control method of PCS for sodium salt energy storage system provided by the present invention. Figure 7 This is a structural diagram of a sodium salt energy storage system, a specific application example of the present invention. Figure 8 This is a schematic diagram of the power conversion main circuit of the PCS of the present invention; In the attached figures, the following labels are used: 1-Sodium salt energy storage system PCS parallel control device; 10-Communication interaction circuit; 11-Drape control circuit; 110 - Virtual impedance compensation unit; 12-Current sharing regulation circuit; 13-Sodium Salt Battery Adapter Circuit; 2 PCS; 20 - Local controller; 21-Sampling circuit; 22-Communication interface; 23-Power conversion main circuit; 30 - Low-speed communication bus; 40-Sodium Salt Battery Management System; Steps S10~S50, S21~S24, S51~S53. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0024] The purpose of this invention is to provide a highly reliable, high-precision, highly adaptable, and easily expandable PCS parallel control method: circulating current is suppressed to within 1% of the rated current; current sharing accuracy is ±2% and dynamic response is <200ms; it deeply couples the characteristics of the 720V sodium salt battery system, extending the system's full life cycle; it supports "plug and play" modules, enabling non-stop maintenance and flexible capacity expansion.

[0025] like Figure 1 As shown in the diagram, an embodiment of the present invention provides a connection diagram of a parallel control device 1 for a sodium salt energy storage system PCS. This parallel control device 1 is integrated into the local controller 20 of each PCS (energy storage converter) 2, and includes a communication interaction circuit 10, a droop control circuit 11, a current sharing regulation circuit 12, and a sodium salt battery adaptation circuit 13. Each PCS 2 also includes a sampling circuit 21 and a communication interface 22.

[0026] The communication interaction circuit 10 is connected to the communication interface 22 and, through the communication interface 22, to the low-speed communication bus 30. It is used to synchronize the voltage frequency reference values ​​of each PCS2 and to obtain the system average current. The droop control circuit 11 is connected to the sampling circuit 21 and is used to generate an initial voltage reference command based on the output current and output voltage of the PCS2. The droop control circuit 11 integrates a virtual impedance compensation unit 110, which generates a compensation amount based on the output current and superimposes it onto the droop control equation. The current sharing adjustment circuit 12 is connected to both the droop control circuit 11 and the communication interaction circuit 10. It is used to fine-tune the initial voltage reference command based on the deviation between the output current of the PCS2 and the system average current, generating the final voltage reference command. The sodium-ion battery adapter circuit 13 is communicatively connected to the sodium-ion battery management system 40 and is used to adjust the droop control coefficient of the droop control circuit 11 based on the received sodium-ion battery state parameters.

[0027] Based on the above-mentioned sodium salt energy storage system PCS parallel control device 1, such as Figure 2 As shown, the parallel control method of the sodium salt energy storage system PCS in this embodiment includes the following steps: S10: Connected to the low-speed communication bus via the communication interaction circuit, it synchronizes the voltage and frequency reference values ​​of each PCS and obtains the system average current.

[0028] Specifically, the communication circuits 10 of each PCS2 are interconnected via a highly reliable low-speed communication bus 30. The low-speed communication bus 30 is, for example, a CAN2.0B (1Mbps) or RS485 (Modbus RTU) bus with a communication cycle of 100ms. This low-speed communication bus 30 does not transmit real-time pulse width modulation (PWM) signals or high-frequency voltage and current commands; it is only used for lightweight information exchange, transmitting PCS identifiers (device numbers), output current, status codes, and system mode commands. This low-speed communication bus 30 is used for: broadcasting system operating mode commands (grid-connected / off-grid, charging / discharging); synchronizing the voltage and frequency reference values ​​of each PCS2; transmitting information such as power limits, sodium-ion battery SOC, and fault status of each PCS2; and implementing "democratic current sharing": each PCS2 periodically exchanges output current information, calculates the average current, and fine-tunes its own voltage reference value to bring the output current closer to the average current, achieving high-precision current sharing.

[0029] Each PCS2's communication circuit 10 broadcasts its own output current via the low-speed communication bus 30, while simultaneously receiving current information from other PCSs to calculate the system's average current. When communication is interrupted, the current sharing regulation circuit 12 automatically degrades to independent droop control, achieving degraded operation.

[0030] S20: The droop control circuit generates an initial voltage reference command based on the output current and output voltage of the machine, and superimposes the virtual impedance compensation amount generated based on the output current into the droop control equation; Specifically, the droop control circuit 11 integrates a virtual impedance compensation unit 110. The virtual impedance compensation unit 110 uses a virtual impedance compensation algorithm in the dq coordinate system to generate the following compensation amount (complete version): , in, This indicates the d-axis voltage compensation amount. This represents the q-axis voltage compensation amount, all in V. , These are the d-axis and q-axis components of the output current after Park transformation, respectively, in amperes (A); = 2πf, , represents the angular frequency of the power grid, in rad / s; This represents the virtual resistance value, in Ω (ohms). This represents the virtual inductance value, measured in Henles (H). The above voltage compensation amount... , The voltage loop reference value is superimposed on the voltage and then transformed inversely to generate a PWM modulation wave.

[0031] In this embodiment, the droop control equation refers to the traditional power-voltage (PV) droop equation. Frequency-reactive power (Qf) droop equation , of which Rated voltage, For the rated frequency, This is the active power droop coefficient. This is the reactive power droop factor. To output active power, To output reactive power.

[0032] In other embodiments, for example, a 400V low-voltage sodium salt energy storage system (with resistive lines), the engineering practice often simplifies to a pure virtual resistance scheme (a special case in engineering implementation). The simplified formula for calculating the compensation amount is as follows: , in, Indicates the voltage compensation amount; This represents the effective value of the PCS output current. This simplified scheme reduces computational complexity and is suitable for sodium salt energy storage systems with voltage levels of 400V and below.

[0033] In this embodiment, the range of virtual impedance parameters and the tuning basis are shown in Table 1 below.

[0034] Table 1: Virtual Impedance Parameter Range and Tuning Basis

[0035] In this embodiment, as Figure 3 As shown, the parallel control method for the PCS of a sodium salt energy storage system also includes the following steps: S21: Real-time calculation of circulation amplitude.

[0036] S22: When the circulating current amplitude exceeds the circulating current preset threshold, an incremental signal proportional to the difference between the circulating current amplitude and the circulating current preset threshold is generated, and the virtual resistance value in the virtual impedance compensation is adjusted in a stepwise manner.

[0037] S23: When the circulating current amplitude is lower than the circulating current preset threshold and continues for a preset waiting time, the virtual resistance value will be slowly restored to the initial value.

[0038] In step S22 above, the incremental signal for step-wise adjustment is calculated according to the following formula: , in, For virtual resistance increment, The amplitude of the circulation. Preset threshold for circulation. The scaling factor is used; the step adjustment changes the virtual resistance value step by step at a first rate; the slow callback is performed at a second rate, and the second rate is less than the first rate.

[0039] S24: Temperature compensation. When the ambient temperature is lower than the preset low temperature threshold, the base value of the virtual resistance is increased by a first preset ratio.

[0040] It should be noted that the temperature compensation step S24 and the circulating current adjustment steps S22-S23 both apply to the same virtual resistance value. Temperature compensation is used to adjust the baseline value, while circulation adjustment is a further step-wise adjustment on top of the baseline value.

[0041] The following example, using four 50kW sodium salt systems, illustrates the above process of circulating current detection and virtual resistance adaptive adjustment: Scenario setting: System parameters are AC side rated voltage Rated current of a single unit The measured difference in line resistance was 0.028Ω; initial settings (satisfy During operation, monitoring showed that, for example, the circulating current amplitude between the second PCS (equipment number #2) and the third PCS (equipment number #3) reached 3.8A (5.0%). (Exceeding the threshold by 3%) The dynamic adjustment process is as follows: Circulation current detection: The local controller calculates the circulation current amplitude every 10ms. . This indicates the amplitude of the circulating current, in amperes (A). In the example, it is 3.8A. , This represents the output current of the two PCS (e.g., PCS#2 and PCS#3 in the example); typically, for any two PCS connected in parallel, the circulating current amplitude is half the absolute value of the current difference between the two.

[0042] Triggering adjustment: Continue for 5 cycles, This indicates the rated current; in the example, it is 76A.

[0043] Incremental calculation:

[0044] This represents the virtual resistance increment, in Ω. This is a proportionality coefficient, with units of Ω / A; in the example, it is 0.015Ω / A. This indicates the preset threshold for circulating current (e.g., 3% of rated current), in amperes (A). When the circulating current amplitude exceeds the preset threshold, the increment is calculated using this formula, and the virtual resistance value is adjusted in a stepwise manner. This represents the adjusted virtual resistance value.

[0045] Smooth transition: The virtual resistance value is adjusted in steps at a rate of 0.005Ω / 100ms (i.e., the first rate) to avoid output voltage surges caused by sudden parameter changes. Effect verification: After adjustment, the circulating current decreased to 1.2 seconds. The steady-state value is maintained at 0.9~1.3A. Recovery mechanism: Circulation After 60 seconds, The virtual resistance value will be restored to the base value at a rate of 0.002Ω / 100ms. In other words, when the circulating current amplitude is lower than the circulating current preset threshold and continues for a preset time (such as 60 seconds), the virtual resistance value will be restored to the initial value slowly at a rate of 0.002Ω / 100ms (i.e., the second rate).

[0046] In this embodiment, the virtual resistor Dynamically adjust based on circulating current amplitude to suppress low-frequency circulating current; virtual inductance The values ​​can be preset to fixed values ​​based on line parameters and temperature conditions, or adjusted independently based on the high-frequency harmonic content.

[0047] The adjustment criteria are summarized as follows: Circulation amplitude is the core trigger condition; temperature compensation is based on the ambient temperature being <5°C (i.e., the low-temperature preset threshold). Pre-increase by 15% (i.e., the first proportion); load rate linkage is set to <20% load. The current drops to 0.04Ω; the fault memory records the historical maximum circulating current value as a startup reference.

[0048] The synergistic mechanism with droop control is as follows:

[0049] In the formula, For system-level power distribution (traditional droop control section). For module-level circulating current suppression (virtual impedance compensation section); (Unit: V); Indicates the rated voltage. This represents the active power droop factor (V / W). This indicates the output active power (in W). Indicates the output current; Parameter decoupling is achieved through frequency domain division of labor: virtual impedance suppresses high-frequency circulating current disturbances (>10Hz), while droop control adjusts low-frequency power distribution (<5Hz). Adjustment of the virtual impedance does not affect the droop coefficient. This avoids the deterioration of voltage stability caused by "increasing the droop coefficient to suppress circulating current" in traditional solutions.

[0050] S30: The initial voltage reference command is finely adjusted by the current sharing adjustment circuit based on the deviation between the local output current and the system average current to generate the final voltage reference command. Specifically, the current sharing adjustment circuit 12 adopts a democratic current sharing algorithm, the mathematical expression of which is as follows: , in, This indicates the final voltage reference command, in volts (V). This indicates the initial voltage reference command, in volts (V). This represents the proportionality coefficient, with units of V / A; Represents the average current of the system. This indicates the output current of the machine, in amperes (A).

[0051] That is, the current sharing adjustment circuit 12 obtains the fine adjustment amount by multiplying the difference between the local output current and the system average current by a proportional coefficient, and then adds the fine adjustment amount to the initial voltage reference command to generate the final voltage reference command.

[0052] Each PCS2's current sharing regulation circuit 12 autonomously calculates the average current and fine-tunes the reference voltage without requiring main control arbitration. When communication is interrupted, the current sharing regulation circuit 12 automatically degrades to independent droop control, achieving degraded operation.

[0053] S40: Communicates with the sodium salt battery management system through the sodium salt battery adapter circuit, and adjusts the droop control coefficient according to the received sodium salt battery status parameters.

[0054] Sodium salt battery adapter circuit 13 performs the following steps: Adjust the DC-side voltage operating point of the PCS according to the preset coefficient based on the total voltage of the sodium salt battery; The total power command of the parallel system is allocated proportionally according to the battery's state of charge: in discharge mode, PCS with a higher state of charge is assigned a higher power weight; in charging mode, PCS with a lower state of charge is assigned a higher power weight. At the end of the charging process, when the total battery voltage exceeds the first charging threshold, the system switches to constant voltage charging mode; when the total battery voltage exceeds the second charging threshold, the system switches to trickle charging mode; and when the total battery voltage exceeds the third charging threshold, the system performs a hard cutoff. The third charging threshold is greater than the second charging threshold, and the second charging threshold is greater than the first charging threshold. At the end of the discharge period, when the total battery voltage is lower than the first discharge threshold, the starting power decreases; when the total battery voltage is lower than the second discharge threshold, a soft shutdown is performed; and when the total battery voltage is lower than the third discharge threshold, a hard shutdown is performed. The first discharge threshold is greater than the second discharge threshold, and the second discharge threshold is greater than the third discharge threshold. The power allocation weight is dynamically adjusted based on the differences in the state of charge of each sodium salt battery cluster, so that the differences in the state of charge between clusters converge to a preset target value.

[0055] Specifically, the key parameters of the digital twin model of the built-in battery in the sodium salt battery adapter circuit 13 are shown in Table 2.

[0056] Table 2 Key parameters of the digital twin model of sodium salt batteries

[0057] In Table 2 above, the temperature compensation coefficient is negative, indicating that the voltage drops when the temperature decreases, and the charging cut-off voltage needs to be increased to compensate.

[0058] The sodium salt battery adapter circuit 13 receives battery pack total voltage, SOC, and health status information from the battery management system. Based on the built-in digital twin model and the received battery status parameters, it adjusts the droop control coefficient of the droop control circuit and executes the following intelligent operating point regulation strategy.

[0059] DC-side voltage operating point adjustment: Based on the current total battery voltage, the DC-side voltage operating point of the PCS is dynamically adjusted to ensure that the inverter can still operate efficiently and stably within the range of battery voltage variations.

[0060] End-of-charge protection: When the system voltage exceeds 740V (first charging threshold), it automatically switches to constant voltage charging mode, and the charging current decreases by a ramp (slope -5% / s); when the voltage reaches 748V (second charging threshold), trickle charging is started (≤0.05C); when the voltage reaches 750V (third charging threshold), hard cutoff is executed and an alarm is triggered.

[0061] End-of-discharge protection: When the system voltage is below 610V (first discharge threshold), power attenuation is initiated 10V in advance, and the output power is linearly reduced to 30% in the range of 610V to 600V; when the voltage is below or equal to 602V (second discharge threshold), soft shutdown is performed to retain a safety margin; when the voltage is below or equal to 600V (third discharge threshold), hard cutoff is performed and deep discharge protection is triggered.

[0062] Multi-cluster dynamic balancing: Real-time calculation of the SOC (State of Charge) differences among clusters. Based on the battery SOC, adaptively adjust the total power command allocation of the parallel system composed of multiple PCS (Power Control Systems) to prevent overcharging or over-discharging. Real-time calculation of the SOC differences among sodium-ion battery clusters; during discharge, clusters with higher SOC are assigned a higher power weight, with a weighting coefficient = 1 + 0.3 × ΔSOC, where... This represents the difference (positive or negative) between the SOC of a battery cluster and the system average SOC, expressed in %; during charging, reverse adjustment is applied (i.e., lower SOC clusters are assigned a higher power weight) to bring the SOC difference between clusters to a preset target value (e.g., 3%). The implicit relationship in actual power allocation is that the power command for a cluster is proportional to its weighting coefficient. The equalization process smoothly embeds the power command, resulting in no output fluctuations.

[0063] In this embodiment, in addition to the control steps (steps S10~S40) that are executed periodically as described above, such as Figure 4 and Figure 5 As shown, the parallel control method for the PCS of the sodium salt energy storage system also includes the following steps: S50: Redundancy management logic, which is triggered when the system starts up, a module fails and exits, or a new module is put into operation. Specifically, it includes: S51: Broadcasts its own device number and health status via low-speed communication bus 30, and dynamically elects a master coordinating PCS based on the health status and device number; S52: When a PCS failure or new PCS is detected, the power command is redistributed. S53: When a new PCS is detected, a smooth cut-in process is triggered.

[0064] The fault exit sequence includes: after fault detection, the control PCS will ramp its output power to zero at a first preset rate (e.g., 10% / s); after the power is reduced to zero, the AC side circuit breaker will be disconnected; at the same time, a fault offline message will be broadcast through the low-speed communication bus 30; after the other PCS receives the fault offline message, it will redistribute the power command according to the state of charge ratio.

[0065] The smooth cut-in process includes: enabling the newly added PCS to detect the AC bus voltage and synchronize with the local output voltage until the amplitude difference is less than the first preset amplitude difference (e.g., 5%), the frequency difference is less than the first preset frequency difference (e.g., 0.1Hz), and the phase difference is less than the first preset phase difference (e.g., 5°); after synchronization is completed, enabling the newly added PCS to send a grid connection request through the low-speed communication bus 30; after receiving the redistributed power command, closing the AC side circuit breaker and controlling the output power to ramp up to the target value at a second preset rate (e.g., 5% / s).

[0066] Specifically, the dynamic master coordinator election is based on PCS health (no faults + SOC 30%~70%) and ID priority, with an election time of <800ms; the disturbance-free fault exit is achieved by the faulty PCS sending an exit command, the power ramp returning to zero (10% / s), the contactor being disconnected, and the system redistributing power; the smooth module input involves the new PCS phase-locked synchronization, receiving system parameters, the power ramp rising (5% / s), and seamless integration into the current sharing system; hot-swapping is supported, and the hardware design includes a pre-charge circuit and soft-start logic to avoid switching shocks.

[0067] The following is combined with Figure 6 The timing process of PCS failure exit and new PCS commissioning is explained in detail.

[0068] Initial state (t0): Module A is running and bears the entire load; Module B is in standby state (hot standby or cold standby) and has not yet participated in power supply; the bus voltage is at the rated value; the system power is at the rated value (supply and demand are balanced); the system is in normal operating state.

[0069] Fault Occurrence and Confirmation (t1 ~ t2): At time t1, a fault occurs inside Module A (such as short circuit, overcurrent, or device damage); the bus voltage begins to drop temporarily, and the system power supply experiences a shortfall (due to the reduced output capacity of A). At time t2, the protection system confirms the fault (e.g., through voltage and current criteria); Module A enters a locked state (output is prohibited, preparing to exit).

[0070] Fault clearance and standby startup (t3): At time t3, Module A performs a disconnection operation (such as circuit breaker tripping) and is electrically isolated from the bus. At this time, the bus is maintained only by possible energy storage or residual voltage, and the voltage and power continue to decrease. At the same time, Module B starts up and enters the "pre-charge" stage from "standby" (charging the DC bus capacitor or filter to avoid grid connection impact).

[0071] Pre-synchronization and grid connection (t4 ~ t5): At time t4, Module B completes pre-charging and enters the "pre-synchronization" stage; it detects the voltage amplitude, frequency, and phase of the bus; by adjusting its own output voltage (e.g., using a phase-locked loop (PLL), it ensures that the difference between its output voltage and the bus voltage meets the grid connection conditions (amplitude difference, frequency difference, and phase difference are within the allowable range). At time t5, the synchronization conditions are met, and grid connection is successful; the grid connection switch of Module B closes, and it begins to output power to the bus; the bus voltage begins to recover from the temporary dip, and the system power gap gradually narrows.

[0072] Restoration to Stability (t6): At time t6, the system enters a new steady state; Module B fully takes over the load, and the operating state changes to "stable". The bus voltage returns to its rated value, and the system power returns to its rated value (the gap is filled). The entire switching process is complete, and the system resumes normal operation.

[0073] The key electrical principles are summarized in Table 3 below.

[0074] Table 3 Key Electrical Principles

[0075] Based on actual measurements, the main performance indicators of the technical solution of this invention are compared as shown in Table 4 below: Table 4: Quantitative Comparison Table

[0076] Furthermore, the technical solution of this invention can be adapted to other high-voltage battery systems such as lead-acid and flow batteries, and the algorithm can be deployed on mainstream DSP platforms such as TIC2000 and STM32H7, supporting software upgrades for existing PCS hardware platforms. This invention meets the GB / T 36276-2018 energy storage safety standard and can effectively reduce the risks of overcharging / over-discharging.

[0077] To facilitate understanding of the above embodiments, a specific application scenario of the above embodiments will be used as an example for explanation below.

[0078] like Figure 7 As shown below, the parallel control method of PCS in the above sodium salt energy storage system will be specifically explained using four 50kW PCS (PCS#1, PCS#2, PCS#3, and PCS#4) connected in parallel to a 720V sodium salt battery system as an example.

[0079] (1) System configuration: On the AC side, four 50kW PCS units are connected in parallel to the 380V bus; on the DC side, each PCS is connected to an independent 720V sodium salt battery cluster (operating range 600~750V) through a combiner cabinet. Each sodium salt battery cluster consists of 10 sodium salt battery packs connected in series, and each battery pack contains approximately 28 sodium salt battery cells connected in series. Each sodium salt battery cluster has a total of 280 sodium salt battery cells connected in series, with a nominal voltage of 720V. Figure 7 "Battery pack *10" indicates 10 sodium salt battery packs; communication is via CAN2.0B bus (1Mbps, 100ms cycle). In this embodiment, the key parameters of the sodium salt battery system are shown in Table 5 below, and the CAN communication message format is shown in Table 6 below.

[0080] Table 5 Key parameters of the sodium salt battery system

[0081] Among them, the temperature compensation coefficient is used to increase the virtual resistance base value under low temperature conditions, the low temperature internal resistance multiplication characteristic is used to dynamically compensate the virtual impedance reference value, and the inter-cluster equalization target is used for SOC equalization control when multiple clusters are running.

[0082] Table 6. Examples of CAN communication message formats (CAN2.0B)

[0083] The module status message period is 100ms, used by each PCS to broadcast its local status; the current sharing instruction message period is 100ms, used to broadcast the system average current and the master coordinator ID; the fault alarm message is event-triggered, used to quickly notify other PCS in case of a fault.

[0084] (2) Start-up phase: After each PCS is powered on, it performs a self-test, including DC side voltage detection (currently 718V); after the self-test, it broadcasts status information through the CAN bus. PCS#1 with ID=1 is selected as the main coordinator. After the main coordinator completes the synchronization phase lock, the power of each PCS starts in a ramp manner, increasing from 0 to 50kW within 5 seconds. (3) Steady-state operation: After the system enters steady state, each PCS exchanges output current data every 100ms via the CAN bus, performing democratic current sharing control. The current output power is stable at 49.8kW±0.9kW. The sodium-ion battery adapter circuit monitors the cluster voltage in real time (currently 715V, SOC≈48%) and dynamically adjusts the DC-side voltage operating point. The virtual impedance compensation unit continuously monitors the circulating current (currently 0.8A) to maintain the virtual resistance value. .

[0085] Temperature compensation: When the ambient temperature is below a preset threshold (e.g., 5°C), the system automatically increases the virtual resistance base value by a first preset percentage (e.g., 15%). For example, when the ambient temperature drops to -5°C, the system will... The resistance was increased from 0.06Ω to 0.069Ω (+15%) to compensate for the increased internal resistance of sodium-ion batteries at low temperatures.

[0086] In this embodiment, the flow equalization adjustment coefficient is adjusted according to the following steps.

[0087] Basic parameter settings: Initial scaling factor is (Democratic equalization); the basic value of virtual impedance (calculated according to Table 7) is: .

[0088] Table 7

[0089] Dynamic response test: The system runs at full load (4x50kW); simulate disturbance, suddenly unload 50% of the load (2 PCS units shut down); observe the circulating current dynamics. If the convergence time is >500ms, appropriately increase the proportional coefficient of the current sharing regulation circuit. (+0.0005V / A each time); if oscillation occurs (circulating current fluctuation > ±0.5A), then reduce... The goal is for the circulation to converge to <1.5A within 300ms.

[0090] Low-temperature operating condition verification: When the ambient temperature is <-10°C, check... Automatically upgrade to .

[0091] Recording and solidification: Record the optimal parameters, write the parameters into the PCS non-volatile memory, and label it "Dedicated to 720V sodium salt system".

[0092] Virtual impedance adaptive adjustment follows this logic: Real-time sampling of the output current of each PCS, and calculation of the circulating current amplitude. ;judge Does it continuously exceed the threshold? (Default 3%) If the limit is exceeded, it will be calculated proportionally. Step-by-step adjustment Monitor the convergence of the circulating flow; if the target is met, record the parameters; if the convergence fails to occur within the time limit, initiate fault diagnosis; if the circulating flow remains at the target for more than 60 seconds, slowly revert to the baseline value; record the adjustment log throughout the process for operation and maintenance analysis and parameter optimization.

[0093] (4) Fault Scenario: When PCS#3 detects an internal overheating fault, it immediately sends an exit message, and the output power ramps to zero within 5 seconds. At the same time, the AC side circuit breaker is disconnected. After receiving the fault offline message, the other three PCS trigger power redistribution within 100ms, redistributing the total power command according to the SOC ratio, increasing the output power of each by 16.7kW. The system maintains a stable output of 150kW. Simultaneously, the virtual impedance parameters are updated synchronously, and the battery management unit recalculates the inter-cluster equalization strategy.

[0094] (5) Low-temperature operation verification: When the ambient temperature drops to -10°C, the battery internal resistance increases, resulting in an initial circulating current of 4.2A. After the virtual impedance compensation unit detects that the circulating current exceeds the limit, it calculates the increment according to the incremental formula and adjusts the virtual resistance value in a stepwise manner at the first rate. The virtual resistance value is adjusted within 1.5 seconds. Adjusted to 0.095Ω; circulating current stabilized at 1.3A (1.7%). The system continuously outputs full power; at the same time, the battery management unit synchronously increases the charging cutoff voltage compensation value to avoid insufficient charging at low temperatures.

[0095] The following are apparatus embodiments corresponding to the above method embodiments. This embodiment can be implemented in conjunction with the above embodiments. The relevant technical details mentioned in the above embodiments remain valid in this embodiment, and will not be repeated here to reduce repetition. Correspondingly, the relevant technical details mentioned in this embodiment can also be applied to the above embodiments.

[0096] This invention also provides a parallel control device 1 for a sodium salt energy storage system PCS, used to execute the above-described parallel control method for a sodium salt energy storage system PCS.

[0097] like Figure 8 As shown, the main power conversion circuit 23 of the PCS includes two parts: a DC side and an AC side. DC side: BAT+ and BAT- are the DC input terminals of the sodium-ion battery cluster. The DC side is equipped with a DC fuse 230 and a DC relay 231 for overcurrent protection and on / off control. The DC bus 232 collects DC power and connects to the bidirectional converter 233. AC side: The bidirectional converter 233 converts DC power into AC power. Its output passes sequentially through an AC filter circuit 234 (filtering out switching ripple and harmonics), an AC relay 235 (grid-connected / off-grid switching control), and an AC fuse 236 (overcurrent protection), finally connecting to the three-phase AC bus (L1, L2, L3, N).

[0098] like Figure 1 As shown, the parallel control device 1 of the sodium salt energy storage system PCS is integrated into the local controller 20 of each PCS2, and includes a communication interaction circuit 10, a droop control circuit 11, a current sharing regulation circuit 12, and a sodium salt battery adapter circuit 13. Each PCS2 also includes a sampling circuit 21 and a communication interface 22.

[0099] The communication interaction circuit 10 is connected to the communication interface 22 and, through the communication interface 22, to the low-speed communication bus 30. It is used to synchronize the voltage frequency reference values ​​of each PCS2 and to obtain the system average current. The droop control circuit 11 is connected to the sampling circuit 21 and is used to generate an initial voltage reference command based on the output current and output voltage of the PCS2. The droop control circuit 11 integrates a virtual impedance compensation unit 110, which generates a compensation amount based on the output current and superimposes it onto the droop control equation. The current sharing adjustment circuit 12 is connected to both the droop control circuit 11 and the communication interaction circuit 10. It is used to fine-tune the initial voltage reference command based on the deviation between the output current of the PCS2 and the system average current, generating the final voltage reference command. The sodium-ion battery adapter circuit 13 is communicatively connected to the sodium-ion battery management system 40 and is used to adjust the droop control coefficient of the droop control circuit 11 based on the received sodium-ion battery state parameters.

[0100] The specific functions and working processes of the above circuits have been described in detail in the method embodiments, and will not be repeated here.

[0101] Another embodiment of the present invention provides a sodium salt energy storage system (such as...) Figure 7 This includes: multiple sodium-ion battery clusters and corresponding sodium-ion battery management systems; at least two PCSs, each PCS including, for example... Figure 1 The sodium salt energy storage system PCS parallel control device 1 is shown, and the DC side of each PCS is connected to a sodium salt battery cluster; a low-speed communication bus connects all PCS; and the AC sides of all PCS are connected in parallel to the same AC bus.

[0102] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms fall within the scope of protection of the present invention.

Claims

1. A parallel control method for a sodium salt energy storage system PCS, characterized in that, Applied to sodium salt energy storage systems comprising at least two PCS units; including: It is connected to a low-speed communication bus through a communication interaction circuit to synchronize the voltage and frequency reference values ​​of each PCS and obtain the system average current. The droop control circuit generates an initial voltage reference command based on the machine's output current and output voltage, and superimposes a virtual impedance compensation amount generated based on the output current into the droop control equation; it calculates the circulating current amplitude in real time; when the circulating current amplitude exceeds the circulating current preset threshold, it generates an incremental signal proportional to the difference between the circulating current amplitude and the circulating current preset threshold, and adjusts the virtual resistance value in the virtual impedance compensation amount in a stepwise manner; when the circulating current amplitude is lower than the circulating current preset threshold and continues for a preset waiting time, it slowly restores the virtual resistance value to its initial value; temperature compensation includes: when the ambient temperature is lower than a low temperature preset threshold, it increases the base value of the virtual resistance value by a first preset ratio; The initial voltage reference command is finely adjusted by the current sharing adjustment circuit based on the deviation between the local output current and the system average current to generate the final voltage reference command. The sodium salt battery adapter circuit communicates with the sodium salt battery management system and adjusts the droop control coefficient according to the received sodium salt battery status parameters. The incremental signal for the step-wise adjustment is calculated using the following formula. ， in, For virtual resistance increment, The amplitude of the circulation. Preset threshold for circulation. The scaling factor is used; the step adjustment changes the virtual resistance value step by step at a first rate; the slow callback is performed at a second rate, and the second rate is less than the first rate.

2. The parallel control method for a sodium salt energy storage system PCS according to claim 1, characterized in that, The communication cycle of the low-speed communication bus is 100ms; when communication is interrupted, the current sharing regulation circuit automatically degrades to independent droop control to achieve degraded operation.

3. The parallel control method for a sodium salt energy storage system PCS according to claim 1, characterized in that, The sodium salt battery adapter circuit performs the following steps: Adjust the DC-side voltage operating point of the PCS according to the preset coefficient based on the total voltage of the sodium salt battery; The total power command of the parallel system is allocated proportionally according to the battery's state of charge: in discharge mode, PCS with a higher state of charge is assigned a higher power weight; in charging mode, PCS with a lower state of charge is assigned a higher power weight. At the end of the charging process, when the total battery voltage exceeds the first charging threshold, the system switches to constant voltage charging mode; when the total battery voltage exceeds the second charging threshold, the system switches to trickle charging mode; and when the total battery voltage exceeds the third charging threshold, the system performs a hard cutoff. At the end of the discharge period, when the total battery voltage is lower than the first discharge threshold, the starting power decreases; when the total battery voltage is lower than the second discharge threshold, a soft shutdown is performed; and when the total battery voltage is lower than the third discharge threshold, a hard shutdown is performed. The power allocation weight is dynamically adjusted based on the differences in the state of charge of each sodium salt battery cluster, so that the differences in the state of charge between clusters converge to a preset target value.

4. The parallel control method for a sodium salt energy storage system PCS according to claim 1, characterized in that, It also includes redundancy management logic, including: The device broadcasts its own device number and health status through the low-speed communication bus, and dynamically elects a master coordinating PCS based on the health status and device number. When a PCS failure or new PCS is detected, a power command reallocation is triggered. When a new PCS is detected, a smooth cut-in process is triggered.

5. The parallel control method for a sodium salt energy storage system PCS according to claim 4, characterized in that, The timing sequence for the fault exit includes: After fault detection, the fault-controlling PCS will ramp the output power to zero at a first preset rate. After the power is reduced to zero, disconnect the AC side circuit breaker; Simultaneously, a fault offline message is broadcast via the low-speed communication bus; After receiving the fault offline message, the remaining PCS redistribute power commands according to the state of charge ratio. The smooth cut-in process includes: enabling the newly deployed PCS to detect the AC bus voltage and synchronize with the local output voltage until the amplitude difference is less than the first preset amplitude difference, the frequency difference is less than the first preset frequency difference, and the phase difference is less than the first preset phase difference; after synchronization is completed, enabling the newly deployed PCS to send a grid connection request through the low-speed communication bus; after receiving the redistributed power command, closing the AC side circuit breaker and controlling the output power to ramp up to the target value at a second preset rate.

6. A parallel control device for a sodium salt energy storage system PCS, characterized in that, For executing the parallel control method of the sodium salt energy storage system PCS as described in any one of claims 1 to 5, each of the PCS includes a local controller, a sampling circuit, and a communication interface; the parallel control device of the sodium salt energy storage system PCS is integrated in the local controller and includes: A communication interaction circuit is connected to the communication interface and, through the communication interface, to a low-speed communication bus for synchronizing the voltage and frequency reference values ​​of each PCS and obtaining the system average current. A droop control circuit, connected to the sampling circuit, is used to generate an initial voltage reference command based on the output current and output voltage of the PCS. The droop control circuit integrates a virtual impedance compensation unit, used to generate a virtual impedance compensation amount based on the output current and superimpose it onto the droop control equation. The virtual impedance compensation unit is also used for: real-time calculation of the circulating current amplitude; when the circulating current amplitude exceeds a preset circulating current threshold, generating an incremental signal proportional to the difference between the circulating current amplitude and the preset circulating current threshold, and adjusting the virtual resistance value in the virtual impedance compensation amount in a stepwise manner; when the circulating current amplitude is lower than the preset circulating current threshold and a preset waiting time is maintained, slowly restoring the virtual resistance value to its initial value; temperature compensation includes: when the ambient temperature is lower than a preset low temperature threshold, increasing the base value of the virtual resistance value by a first preset ratio. The current sharing adjustment circuit is connected to the droop control circuit and the communication interaction circuit respectively, and is used to fine-tune the initial voltage reference command according to the deviation between the output current of the PCS and the average current of the system, and generate the final voltage reference command. A sodium salt battery adapter circuit, which is communicatively connected to the sodium salt battery management system, is used to adjust the droop control coefficient of the droop control circuit according to the received sodium salt battery status parameters. The incremental signal for the step-wise adjustment is calculated using the following formula. ， in, For virtual resistance increment, The amplitude of the circulation. Preset threshold for circulation. The scaling factor is used; the step adjustment changes the virtual resistance value step by step at a first rate; the slow callback is performed at a second rate, and the second rate is less than the first rate.

7. A sodium salt energy storage system, characterized in that, include: Multiple sodium salt battery clusters and corresponding sodium salt battery management systems; At least two PCS, each PCS including the sodium salt energy storage system PCS parallel control device as described in claim 6, and the DC side of each PCS is connected to the sodium salt battery cluster; a low-speed communication bus connecting all the PCS; and the AC sides of all PCS are connected in parallel to the same AC bus.

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