Off-grid parallel operation starting method of energy storage system, energy storage system and storage medium

Abstract

The invention relates to an off-grid parallel operation starting method of an energy storage system, the energy storage system and a storage medium, and belongs to the technical field of energy storage. The host receives the phase locking synchronization completion signal and sends a voltage unification instruction to the slave after determining that the grid-connected slave completes phase locking synchronization, and the host and the slave are boosted from the black start voltage to the rated voltage based on the voltage unification instruction to complete parallel start, so that fluctuation caused by unstable voltage in the start process of the slave can be improved; the stability of the energy storage system in the off-grid parallel operation process is improved; the slave is started after being synchronized according to the black start voltage phase lock phase established by the host, so that the output voltage after the slave is started is consistent with the output voltage of the host, the voltage consistency of the parallel energy storage current device is high, ring current caused by voltage difference can be reduced, and the operation efficiency of the system is improved; and the slave is started after successful phase locking, so that the risk of starting failure can be reduced.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to an off-grid parallel startup method for an energy storage system, an energy storage system, and a storage medium. Background Art

[0002] With the development of energy storage and power grid, energy storage inverters are crucial in off-grid applications. However, due to design and cost limitations, single-machine energy storage inverters are difficult to meet the needs of large-scale energy storage or high-power loads. Parallel connection of multiple machines can improve the performance of energy storage systems, but technical problems such as stable start and stop, circulation, command synchronization and load balancing need to be solved. Improper handling will affect system stability and equipment safety.

[0003] The existing off-grid multi-machine parallel control method of energy storage converter is imperfect and has many problems, which may lead to safety hazards. Summary of the invention

[0004] Based on this, it is necessary to provide an off-grid parallel startup method, an energy storage system and a storage medium for the above-mentioned technical problems.

[0005] In a first aspect, the present application provides an off-grid parallel startup method for an energy storage system, which is used to realize synchronous parallel operation of multiple energy storage converters of the energy storage system in an off-grid mode, wherein the multiple energy storage converters include a master and at least one slave, and the method includes:

[0006] After the host determines that the slave receives the start instruction, the host starts;

[0007] The host performs DC side pre-charging, closes the AC relay after pre-charging is completed, establishes and outputs a black start voltage, and sends a voltage phase-locked synchronization start instruction to the slave;

[0008] After receiving the voltage phase phase lock synchronization start instruction, the slave performs voltage and phase synchronization with the host with reference to the black start voltage, and sends a phase lock synchronization completion signal to the host after synchronization is completed;

[0009] After the host receives the phase-locked synchronization completion signal and determines that the grid-connected slaves have all completed phase-locked synchronization, the host sends a voltage unification instruction to the slaves. Based on the voltage unification instruction, the host and the slaves are boosted from the black start voltage to the rated voltage to complete the parallel startup.

[0010] Optionally, during the startup process, the host obtains the current active power and the current reactive power of each of the energy storage converters connected to the grid, and obtains the average active power and the average reactive power of the energy storage converters connected to the grid;

[0011] The host sends the active power average value and the reactive power average value to each of the slaves;

[0012] The slave receives the active power mean value and the reactive power mean value sent by the host, and the slave adjusts power according to the active power mean value and the reactive power mean value.

[0013] Optionally, the host is started in a voltage-frequency control mode, and the host controls voltage and current through an outer voltage loop and an inner current loop;

[0014] The outer voltage loop of the host adjusts the output voltage of the host according to a voltage set value and a voltage feedback signal, and the outer voltage loop outputs a current instruction to the inner current loop;

[0015] The inner current loop adjusts the current of the host according to the current command and the current feedback signal.

[0016] Optionally, the voltage control of the slave adopts a power-current control mode, and the slave controls power and current through an outer power loop and an inner current loop to adjust the output voltage of the slave;

[0017] The outer power loop adjusts the power of the slave according to a power given value and a power feedback signal, and the outer power loop outputs a current instruction to the inner current loop;

[0018] The inner current loop of the slave adjusts the current of the slave according to the current command and the current feedback signal of the slave.

[0019] Optionally, while the slave performs voltage and phase synchronization, the slave uses the active power average value and the reactive power average value as the power set value of the outer power ring.

[0020] Optionally, when the host performs DC side pre-charging, the output voltage of the host is linearly ramped up from 0V to the black start voltage.

[0021] Optionally, the host adopts a linear ramp boost control so that the host and the slave are boosted from the black start voltage to the rated voltage in a linear ramp.

[0022] Optionally, the linear ramp voltage increase has a voltage increase rate lower than 20V / ms.

[0023] In a second aspect, the present application provides an energy storage system, comprising a plurality of parallel energy storage inverters and a controller, wherein the plurality of energy storage inverters include a host and at least one slave, and the controller includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores a computer program executable by the at least one processor, and the computer program is executed by the at least one processor so that the at least one processor can execute the off-grid parallel startup method of the energy storage system described in the first aspect, to realize the synchronous parallel operation of the plurality of energy storage inverters of the energy storage system in the off-grid mode.

[0024] In a third aspect, the present application provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the off-grid parallel startup method of the energy storage system described in the first aspect is implemented.

[0025] The off-grid parallel startup method, energy storage system and storage medium of the above-mentioned energy storage system are as follows: after the host determines that the slave has received the startup instruction, the host starts; the host performs DC side pre-charging, closes the AC relay after the pre-charging is completed, the host establishes and outputs the black start voltage, and sends a voltage phase-locked synchronization start instruction to the slave; after the slave receives the voltage phase-locked synchronization start instruction, it synchronizes the voltage and phase with the host with the black start voltage as a reference, and sends a phase-locked synchronization completion signal to the host after the synchronization is completed; the host receives the phase-locked synchronization completion signal, and after determining that the grid-connected slaves have completed the phase-locked synchronization, the host sends a voltage unification instruction to the slave, and the host and the slave are boosted from the black start voltage to the rated voltage based on the voltage unification instruction to complete the parallel startup. The host starts first and establishes a stable black start voltage to provide a stable reference voltage source for the phase-locked synchronization of the slave. During the startup process, the slave synchronizes the voltage and phase according to the black start voltage, and then the host and the slave jointly boost the black start voltage to the rated voltage in two stages, which can improve the fluctuation caused by voltage instability during the startup of the slave, which is beneficial to improving the stability of the energy storage system during the off-grid parallel process; the slave is started after phase-locked synchronization according to the black start voltage phase established by the host, so that the output voltage of the slave after startup is consistent with the output voltage of the host. The voltage consistency of the energy storage current meter of the parallel machine is high, which can reduce the circulating current caused by voltage difference and improve the operation efficiency of the system; the slave starts after successful phase locking, which is beneficial to reduce the risk of startup failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technologies, the drawings required for use in the embodiments or the related technical descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 A schematic flow chart of an off-grid parallel startup method for an energy storage converter in one embodiment;

[0028] Figure 2 A voltage-frequency control block diagram of a host in one embodiment;

[0029] Figure 3 is an active power-active current control block diagram of a slave in one embodiment;

[0030] Figure 4 A reactive power-reactive current control block diagram of a slave in one embodiment;

[0031] Figure 5 A schematic flow chart of an off-grid parallel startup method for an energy storage converter in another embodiment;

[0032] Figure 6 is a block diagram of an energy storage system in one embodiment;

[0033] Figure 7 FIG. 4 is a diagram showing the internal structure of a controller of an energy storage system in one embodiment. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0035] At present, the commonly used off-grid parallel startup method of energy storage converters mainly adopts droop control to achieve power sharing. Droop control distributes load power through linear droop of active power-frequency (P-ω) and reactive power-voltage (QV), so that each converter can dynamically adjust the output characteristics according to the output power to achieve load distribution. However, this method may have defects such as uneven power distribution of droop control due to line impedance difference, limited phase synchronization accuracy of each unit, resulting in phase deviation and exciting circulating current between parallel units, and uneven thermal stress distribution caused by long-term operation of the converter in an overload state.

[0036] In the related technology, the off-grid parallel starting method of the energy storage inverter also includes power sharing control based on virtual impedance. Although it can improve the steady-state power distribution, it has slow dynamic response and relies on precise parameter setting. The related technology also uses communication-assisted control, which can achieve precise synchronization but increases the system complexity and single-point failure risk.

[0037] There is an urgent need to provide an efficient and reliable parallel control method for multi-machine autonomous synchronization of converters, optimize the control strategy, improve system synchronization, and ensure the stable operation of the multi-machine parallel system.

[0038] In an exemplary embodiment, Figure 1 As shown, a method for starting an energy storage system in parallel off the grid is provided. The method is applied to the energy storage system and is suitable for scenarios where multiple energy storage converters of the energy storage system need to work together in an off-grid mode, such as an island microgrid, a power supply system in a remote area, etc. It is used to realize the synchronous parallel operation of multiple energy storage converters of the energy storage system in an off-grid mode, and the multiple energy storage converters include a master and at least one slave. The method for starting an energy storage system in parallel off the grid in this embodiment includes the following steps 101 to 104.

[0039] Step 101: After the host determines that the slave has received the start instruction, the host starts.

[0040] In this embodiment, the host PCS_Master sends a startup instruction to multiple slave PCS_Slave through internal communication (such as CAN bus, Ethernet, etc.). After receiving the startup instruction, the slave PCS_Slave performs initialization operations to prepare to enter the off-grid parallel mode. After the slave PCS_Slave completes the initialization, it sends a confirmation signal to the host PCS_Master through the internal communication channel, or the slave PCS_Slave can send a confirmation frame to the PCS_Master, indicating that it is ready to enter the off-grid parallel mode. After the host PCS_Master receives the confirmation signal or confirmation frame from the slave PCS_Slave, the host PCS_Slave starts to enter the off-grid parallel mode. The host PCS_Master starts to enter the off-grid parallel mode only after receiving the confirmation signals from all the slave PCS_Slave of the energy storage system. Alternatively, the host PCS_Master receives the slave PCS_Slave that has sent the confirmation signal within the preset time period, and counts the number of the slave PCS_Slave that has sent the confirmation signal within the preset time period. The host PCS_Master controls the slave PCS_Slave that has sent the confirmation signal within the preset time period to enter the off-grid parallel mode.

[0041] Step 102: The host performs pre-charging on the DC side, and after the pre-charging is completed, the AC relay is closed, the host establishes and outputs a black start voltage, and sends a voltage phase-locked synchronization start instruction to the slave.

[0042] In this embodiment, the host PCS_Master slowly charges the DC side capacitor through the internal pre-charging circuit to avoid excessive transient current when the system is powered on. When the voltage of the DC side capacitor reaches a predetermined value (such as 80% or 90% of the system operating voltage), the pre-charging is completed and the host PCS_Master ends the DC side charging. The host PCS_Master closes the AC relay through a control signal so that the AC power supply supplies power to the load through the AC relay. After the AC relay of the host PCS_Master is closed, the host PCS_Master starts to establish an output voltage to provide the slave PCS_Master with the voltage and current required for startup. After the host PCS_Masterd outputs the black start voltage stably, the host PCS_Masterd outputs the black start voltage to all the slave PCS_Slave to be connected in parallel through the connecting line. At the same time, the host PCS_Master sends a voltage phase lock synchronization start instruction to the slave PCS_Slave through internal communication (such as CAN bus, Ethernet, etc.), instructing the slave PCS_Slave to phase-lock with the PCS_Master according to the black start voltage, so that the slave PCS_Slave starts to phase-lock with the host voltage PCS_Master after receiving the instruction.

[0043] In this embodiment, the black start voltage is 75%-80% of the rated voltage. For example, the black start voltage may be 75%, 76%, 77%, 78%, 79% or 80% of the rated voltage.

[0044] Step 103: After receiving the voltage phase phase lock synchronization start instruction, the slave synchronizes the voltage and phase with the host with the black start voltage as a reference, and sends a phase lock synchronization completion signal to the host after the synchronization is completed.

[0045] In this embodiment, after the slave PCS_Slave receives the voltage phase phase-locked synchronization start instruction, the slave PCS_Slave detects the voltage at its AC input end (i.e., the black start voltage established by the host PCS_Master) as a reference, and synchronizes the voltage and phase with the host PCS_Master. In this embodiment, the slave PCS_Slave adjusts its power and current to adjust its output voltage, so that the output voltage of the slave PCS_Slave gradually approaches and eventually remains consistent with the black start voltage of the host PCS_Master. The slave PCS_Slave will also adjust the waveform and phase of its voltage so that the waveform and phase of the voltage of the slave PCS_Slave are synchronized with the voltage waveform and phase of the host PCS_Master. After the slave PCS_Slave completes the synchronization of voltage and phase with the host PCS_Master, the slave PCS_Slave closes the relay on its AC inverter side so that the inverter of the slave PCS_Slave can output the voltage to the power grid or load. At the same time, the slave PCS_Slave sends a phase-locked synchronization completion signal to the host PCS_Master through internal communication. The slave PCS_Slave starts after the phase-locked synchronization is completed and enters the off-grid parallel mode.

[0046] Step 104: After the host receives the phase-locked synchronization completion signal and determines that all the grid-connected slaves have completed phase-locked synchronization, the host sends a voltage unification command to the slaves. Based on the voltage unification command, the host and the slaves are boosted from the black start voltage to the rated voltage to complete the parallel startup.

[0047] In this embodiment, the host PCS_Master receives a phase-locked synchronization completion signal from each slave PCS_Slave, and the phase-locked synchronization completion signal indicates that the slave PCS_Slave has completed the voltage and phase synchronization lock, and the inverter output of the slave PCS_Slave is consistent with the output of the host PCS_Master in voltage and phase. The host PCS_Master confirms the phase-locked synchronization completion signal of the slave PCS_Slave, and after confirming that all the slave PCS_Slave to be connected to the grid have completed the phase-locked synchronization, the host PCS_Master sends a voltage unification instruction to all the slave PCS_Slave to be connected to the grid, and the voltage unification instruction is used to instruct the energy storage inverter to boost the output voltage from the black start voltage to the rated voltage.

[0048] The host PCS_Master and the slave PCS_Slave synchronously perform the second stage of boosting based on the unified voltage command, and synchronously boost the output voltage from the black start voltage to the rated voltage. After the output voltage of the host PCS_Master and the slave PCS_Slave is stabilized at the rated voltage and the energy storage system is running stably, the off-grid parallel startup of the host PCS_Master and the slave PCS_Slave is completed. At this time, the host PCS_Master and the slave PCS_Slave run in parallel to jointly provide a stable AC voltage for the grid or load.

[0049] The rated voltage is the rated operating voltage of the energy storage system configuration, and is also the output voltage when the master PCS_Master and the slave PCS_Slave operate in parallel.

[0050] In the off-grid parallel startup method for the energy storage system of the above embodiment, the host starts after the host determines that the slave has received the startup instruction; the host performs DC side pre-charging, closes the AC relay after the pre-charging is completed, the host establishes and outputs the black start voltage, and sends a voltage phase phase-locked synchronization start instruction to the slave; after the slave receives the voltage phase phase-locked synchronization start instruction, it synchronizes the voltage and phase with the host with the black start voltage as a reference, and sends a phase-locked synchronization completion signal to the host after the synchronization is completed; the host receives the phase-locked synchronization completion signal, and after determining that the grid-connected slaves have completed the phase-locked synchronization, the host sends a voltage unification instruction to the slave, and the host and the slave are boosted from the black start voltage to the rated voltage based on the voltage unification instruction, completing the parallel startup. The host starts first and establishes a stable black start voltage, providing a stable reference voltage source for the phase-locked synchronization of the slave. During the startup process, the slave synchronizes the voltage and phase according to the black start voltage, and then the host and the slave jointly boost the black start voltage to the rated voltage in two stages, which can improve the fluctuation caused by voltage instability during the startup process of the slave, and is beneficial to improving the stability of the energy storage system during the off-grid parallel operation process; the slave is started after the black start voltage phase is phase-locked and synchronized according to the host, so that the output voltage of the slave after startup is consistent with the output voltage of the host, and the voltage consistency of the parallel energy storage current meter is high, which can reduce the circulating current caused by the voltage difference and improve the operation efficiency of the system; the slave starts after the phase lock is successful, which is beneficial to reduce the risk of startup failure. In the off-grid parallel operation method of the energy storage system of the above embodiment, the master-slave mode makes the system have good scalability and flexibility, and the number of parallel slaves can be increased or decreased according to actual needs to adapt to different load requirements.

[0051] In some embodiments, during the startup process, the host obtains the current active power and current reactive power of each grid-connected energy storage converter, and obtains the average active power and average reactive power of the grid-connected energy storage converter; the host sends the average active power and average reactive power to each slave. The slave receives the average active power and average reactive power sent by the host, and the slave adjusts the power according to the average active power and average reactive power.

[0052] In this embodiment, during the startup process, the host PCS_Master obtains the current active power (P) and reactive power (Q) of the host PCS_Master itself and each grid-connected slave PCS_Slave through internal communication. The host PCS_Master weights the active power and reactive power of the host PCS_Master and each grid-connected slave PCS_Slave to calculate the average active power (P_avg) and average reactive power (Q_avg) of the grid-connected energy storage converter. The average active power (P_avg) and the average reactive power (Q_avg) reflect the overall current power status of the grid-connected energy storage converter. The host PCS_Master sends the average active power (P_avg) and the average reactive power (Q_avg) to each slave PCS_Slave through the communication network. After receiving the average active power (P_avg) and the average reactive power (Q_avg), each slave PCS_Slave adjusts its own active power and reactive power so that the active power and reactive power can approach or reach the average active power (P_avg) and the average reactive power (Q_avg).

[0053] In this embodiment, the host PCS_Master obtains the current active power and reactive power of each grid-connected energy storage inverter during the startup process, calculates the power average and sends it to each slave PCS_Slave, controls each slave PCS_Slave to adjust the output power according to the power average, which can improve the uniformity of power distribution of each slave PCS_Slave, reduce the probability of overload or underload of the slave PCS_Slave, and improve the operating efficiency of the system; improving the uniformity of power distribution of the slave PCS_Slave can also reduce voltage fluctuations and harmonics, and improve the voltage stability of the system.

[0054] In some embodiments, the host is started in a voltage-frequency control mode, and the host controls voltage and current through an outer voltage loop and an inner current loop; the outer voltage loop of the host adjusts the output voltage of the host according to a voltage set value and a voltage feedback signal, and the outer voltage loop outputs a current instruction to the inner current loop; the inner current loop adjusts the current of the host according to the current instruction of the outer voltage loop and the current feedback signal of the host.

[0055] In this embodiment, refer to Figure 2As shown in the figure, the host PCS_Master adopts the voltage-frequency control mode (V / F control mode) to maintain a constant ratio between voltage and frequency so that the torque of the host PCS_Master is stable during the parallel startup process. The host PCS_Master adopts a dual-loop control structure of an outer voltage loop and an inner current loop to collaboratively control the voltage and current, thereby achieving control of the output frequency.

[0056] In this embodiment, refer to Figure 2 As shown in the figure, the outer voltage loop of the host PCS_Master adjusts the output voltage of the host PCS_Master according to the voltage set value and the real-time voltage feedback signal of the host PCS_Master. The voltage set value is usually a preset expected value. The voltage set value of the first stage boost is the black start voltage, and the voltage set value of the second stage boost is the rated voltage. The voltage feedback signal is the monitoring value of the actual output voltage of the host PCS_Master. The proportional integral (PI) controller of the outer voltage loop generates a compensation signal by comparing its actual output voltage with the voltage set value, and adjusts the output voltage in real time according to the compensation signal until the output voltage reference value is stabilized. In this way, the output voltage of the host PCS_Master is stabilized, the DC bus voltage or AC side voltage amplitude is maintained, the impact of load changes or input disturbances on the voltage is reduced, and a stable voltage reference can be provided for the inner current loop. At the same time, the outer voltage loop calculates the current command in real time based on the voltage adjustment requirements, and outputs the current command to the inner current loop of the host PCS_Master.

[0057] In this embodiment, during the startup of the host PCS_Master, the host PCS_Master generates a voltage command feedforward instruction according to the voltage given value, and the voltage command feedforward instruction includes information required to make the output voltage of the host PCS_Master quickly track the voltage given value. The host PCS_Master sends the voltage command feedforward instruction to the inverter of the host PCS_Master, and the inverter controls the frequency and amplitude of the square wave signal according to the voltage command feedforward instruction. In this way, the inverter can ensure that the output voltage of the host PCS_Master is consistent with the voltage given value by accurately controlling the frequency and amplitude of the square wave signal through the inverter, thereby achieving precise voltage control.

[0058] In this embodiment, the inner current loop adjusts the host current according to the current command from the outer voltage loop and the real-time current feedback signal of the host PCS_Master. The host PCS_Master collects its own DC side current in real time, and adjusts the output current according to the current command and the deviation between the current feedback value and the current reference value (generated by the outer voltage loop) through the PI controller of the inner current loop. This stabilizes the output current of the host PCS_Master, thereby quickly suppressing current disturbances, so that the energy storage system can quickly alleviate disturbances caused by sudden loading / unloading.

[0059] In this embodiment, the host PCS_Master adopts a voltage-frequency control mode. Through a dual-loop control structure of an outer voltage loop and an inner current loop, the outer voltage loop adjusts the output voltage to stabilize the output voltage of the host PCS_Master; the inner current loop adjusts the output current according to the DC side current feedback signal to achieve output current stability; the response speed and stability of the off-grid parallel process are improved, and the energy storage system's ability to resist sudden loading / unloading interference is also enhanced.

[0060] In some embodiments, the voltage control of the slave adopts a power-current control mode, and the slave controls power and current through an outer power loop and an inner current loop to adjust the output voltage of the slave. After the slave receives the voltage phase-locked synchronization start instruction, the outer power loop adjusts the power of the slave according to the power set value and the power feedback signal; at the same time, the outer power loop of the slave outputs a current instruction to the inner current loop. The inner current loop of the slave adjusts the current of the slave according to the current instruction of the outer power loop and the current feedback signal of the slave.

[0061] In this embodiment, refer to Figure 3 , Figure 4 As shown in the figure, the slave PCS_Slave adopts the power-current control mode (PQ control mode), and adjusts the output voltage of the slave PCS_Slave by directly controlling the current of the slave PCS_Slave. This control strategy controls the current more directly and quickly, and the response speed of adjusting the output voltage is faster. The slave PCS_Slave adopts a dual-loop control structure of an outer power loop and an inner current loop to control the power and current of the slave PCS_Slave, and then adjust the output voltage of the slave PCS_Slave.

[0062] In this embodiment, the outer power loop adjusts the active power and reactive power of the slave PCS_Slave respectively, and the inner current loop adjusts the active current and reactive current of the slave PCS_Slave respectively.

[0063] Reference Figure 3As shown, the outer power loop of the slave PCS_Slave uses the average active power as the power setting value for active power regulation. The PI controller of the outer power loop compares the average active power given by the host PCS_Master with its own real-time active power feedback signal, detects the phase difference and frequency deviation between the two, and adjusts the phase and amplitude of its output power according to the detection results, so that the active power of the slave PCS_Slave reaches the average active power. The outer power loop calculates the active current command in real time according to the active power adjustment requirements, and outputs the active current command to the inner current loop of the slave PCS_Slave.

[0064] The inner current loop of the slave PCS_Slave receives the active current command and the active current feedback signal of the slave PCS_Slave, the PI controller of the outer power loop compares the active current command and the active current feedback signal of the slave PCS_Slave, calculates the current error, and the inner current loop adjusts the active current of the slave PCS_Slave according to the current error.

[0065] In this embodiment, the slave PCS_Slave generates an active power command feedforward instruction according to the active power given value, and the active power command feedforward instruction includes the pre-information of the active power dynamic regulation, which is used to compensate for the delay and disturbance in the power regulation process. The slave PCS_Slave sends the active power command feedforward instruction to its own inverter, and the inverter generates a PWM modulation signal according to the active power command feedforward instruction. The modulation signal drives the inverter to output a three-phase AC voltage so that its amplitude and frequency meet the power regulation requirements.

[0066] Reference Figure 4 As shown, the outer power loop of the slave PCS_Slave compares the reactive power mean given by the host PCS_Master with its own real-time reactive power feedback signal, and adjusts the phase and amplitude of the reactive power according to the detection result, so that the reactive power of the slave PCS_Slave reaches the reactive power mean. The outer power loop calculates the reactive current command in real time according to the reactive power adjustment requirements, and outputs the reactive current command to the inner current loop of the slave PCS_Slave. The inner current loop calculates the current error according to the reactive current command and the reactive current feedback signal of the slave PCS_Slave, and the inner current loop adjusts the reactive current according to the current error.

[0067] In this embodiment, the slave PCS_Slave generates a reactive power command feedforward instruction according to the reactive power set value, and sends the reactive power command feedforward instruction to its own inverter. The inverter generates a PWM modulation signal according to the reactive power command feedforward instruction. The modulation signal drives the inverter to output a three-phase AC voltage so that its amplitude and frequency meet the power regulation requirements.

[0068] In this embodiment, the slave PCS_Slave adopts a power-current control mode. The slave PCS_Slave coordinates the power and current of the slave PCS_Slave through the outer power loop and the inner current loop, and then adjusts the voltage of the slave PCS_Slave to synchronize the voltage and phase of the slave PCS_Slave with the host PCS_Master, which is beneficial to improving the dynamic response speed of the slave PCS_Slave, reducing the impact of sudden loading / unloading, and improving the stability and reliability of the off-grid parallel process.

[0069] In some embodiments, when the host PCS_Master performs DC side pre-charging, the output voltage of the host PCS_Master is linearly ramped up from 0V to a black start voltage.

[0070] In this embodiment, when the host PCS_Master performs DC side pre-charging, the output voltage of the host PCS_Master is gradually increased by means of a linear ramp boost. The linear ramp boost control can steadily increase the output voltage and reduce the impact on the load.

[0071] In some embodiments, the host uses a linear ramp boost control so that the host and the slave are linearly ramped from the black start voltage to the rated voltage. In this embodiment, the host PCS_Master linear ramp boost control ensures the voltage synchronization between the host PCS_Master and the slave PCS_Slave, improving the stability and reliability of the off-grid parallel process.

[0072] In some embodiments, the boost rate of the linear ramp boost is lower than 20V / ms. This ensures a smooth increase in the output voltage of the host PCS_Master and / or the slave PCS_Slave, and reduces the impact of the sudden output voltage of the host PCS_Master and / or the slave PCS_Slave on the load. For example, the boost rate of the linear ramp boost can be 10V / ms, 12V / ms, 14V / ms, 15V / ms, 16V / ms, 18V / ms, etc.

[0073] In some embodiments, during the parallel startup of the master and slave, when a sudden load is added or removed, the transient voltage deviation of the master and slave recovers to within ±5% of the rated voltage within 100ms.

[0074] The off-grid parallel startup method of the energy storage system of the above embodiment is used to detect the offline parallel startup process of the master and slave machines at a load of 20% and a load of 100%, respectively. The detection results are shown in Tables 1 and 2.

[0075] Table 1 Power and current distribution when the load is 20% (the preset power of a single energy storage converter is 42.5kW)

[0076]

[0077] Table 2 Power and current distribution when load is 100% (preset power of a single energy storage converter is 213kW)

[0078]

[0079] According to Table 1 and Table 2, when the load is 20%, the deviation between the sum of the active power of the master and the active power of the slave and the sum of the preset power is 0.09kW; the active power deviation between the master and the slave is 0.37kW, accounting for 0.87%; the reactive power deviation between the master and the slave is 0.61kW, accounting for 13.5%. The active current deviation is 0.31A; the current imbalance is 0.43%; the reactive current deviation is 0.65A; and the phase synchronization deviation is 1.2°.

[0080] At 100% load, the deviation between the sum of the active power of the master and the active power of the slave and the sum of the preset power is 0.73kW. The active power deviation between the master and the slave is 0.88kW, accounting for 0.50%; the reactive power deviation between the master and the slave is 0.31kW, accounting for 8.6%. The active current deviation is 0.88A; the current imbalance is 0.50%; the reactive current deviation is 0.31A; and the phase synchronization deviation is 0.8°.

[0081] According to the test results, the off-grid parallel starting method of the energy storage system of this embodiment has high active power distribution accuracy, and the system has better power tracking capability under heavy load; the reactive power distribution accuracy is high, and the system responds sensitively under heavy load; the current imbalance is low, the phase synchronization accuracy is high, and the commutation problem can be improved.

[0082] The sudden loading and unloading of the energy storage system in the above embodiment is detected during the off-grid parallel operation.

[0083] The resistive load resistance is 5.59Ω (215kW*2*0.2=86kW, 20% load), the load is suddenly loaded from 20% to 100% load, the resistive load resistance is 5.59Ω (215kW*2, 100% load), the maximum transient voltage deviation within 100ms is 34.2V, which is less than 69V (meeting the national standard test requirements of GBT 34120-2023), and the transient voltage deviation of the host and the slave is restored to within ±5% of the rated voltage within 100ms. Among them, 215kW is the rated power of a single energy storage converter, and 2 indicates that in this embodiment, two energy storage converters, one host and one slave, are started in parallel.

[0084] The resistive load resistance is 1.115Ω (215kW*2, 100% load), the load is suddenly unloaded from 100% to 20% load, the resistive load resistance is 5.59Ω (215kW*2*0.2=86kW, 20% load), the maximum transient voltage deviation within 100ms is 37.7V, which is less than 69V, and the transient voltage deviation between the host and the slave recovers to within ±5% of the rated voltage within 100ms.

[0085] The detection results of the energy storage system of this embodiment during sudden loading and sudden unloading in the off-grid parallel method meet the national standard test requirements of GBT 34120-2023 for electrochemical energy storage system energy storage converters.

[0086] According to an exemplary embodiment, this embodiment provides an off-grid parallel startup method for an energy storage system, which is applied to the energy storage system and is used to realize synchronous parallel operation of multiple energy storage converters of the energy storage system in an off-grid mode, wherein the multiple energy storage converters include a master and at least one slave. Figure 5 As shown, the off-grid parallel startup method of the energy storage system includes the following steps.

[0087] The master starts after receiving the start confirmation signal from the slave through internal communication. The master starts only after receiving the confirmation signal from all slaves within the preset time period, or counts the number of slaves that send confirmation signals within the preset time period and controls them to enter the off-grid parallel mode.

[0088] The host performs pre-charging on the DC side, and after the pre-charging is completed, the AC relay is closed, and the voltage is increased from 0V linearly by a ramp until a stable black start voltage is established. The host sends a voltage phase-locked synchronous start command to the slave; the black start voltage is 75%-80% of the rated voltage; when the host performs pre-charging on the DC side, the output voltage is increased from 0V linearly by a ramp to the black start voltage, and the voltage increase rate is less than 20V / ms. The host adopts a voltage-frequency control mode, and controls the voltage and current through an outer loop voltage loop and an inner loop current loop; the outer loop voltage loop of the host adjusts the output voltage according to the voltage set value and the voltage feedback signal; the inner loop current loop adjusts the current according to the current feedback signal. In this embodiment, the host obtains the current active power and reactive power of the grid-connected energy storage converter during the startup process, calculates the mean active power and reactive power of the grid-connected energy storage converter, and sends the mean to each slave, and the slave adjusts its own output power according to the received power mean.

[0089] The slave uses the black start voltage as a reference to synchronize the voltage and phase with the host. After the slave completes the phase-locked synchronization, it sends a phase-locked synchronization completion signal to the host and closes its AC relay. Among them, the slave adopts the power-current control mode, and controls the power and current through the outer power loop and the inner current loop. The slave adopts the power-current control mode, and controls the power and current through the outer power loop and the inner current loop. The outer power loop of the slave uses the average active power and the average reactive power sent by the host as the power set value of the active power and the reactive power. The outer power loop adjusts the active power and the reactive power according to the power set value and the power feedback signal, so that the active power and the reactive power of the slave can reach the average active power and the reactive power allocated by the host. The outer power loop calculates the active current command and the reactive current command in real time according to the power set value and the power feedback signal deviation, and outputs the active current command and the reactive current command to the inner current loop of the slave. The inner current loop of the slave adjusts the current (active current and reactive current) according to the current command (active current command and reactive current command) and the current feedback signal (active current feedback signal and reactive current feedback signal). By adjusting the power and current, the voltage of the slave is adjusted to reach the given voltage value, so that the voltage phase of the slave is the same as that of the host.

[0090] After the host receives the phase-locked synchronization completion signal from all slaves, it sends a voltage unification command to the slave. After the slave receives the voltage unification command, the host and the slave synchronize to increase the output voltage from the black start voltage to the rated voltage in a linear ramp to complete the parallel start. Among them, the host and the slave jointly increase the voltage from the black start voltage to the rated voltage in a linear ramp. The host and the slave adopt a synchronous linear ramp boost control, and the boost rate is less than 20V / ms.

[0091] It should be understood that, although the steps in the flowcharts involved in the above embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above embodiments may include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0092] Based on the same inventive concept, the embodiment of the present application also provides an energy storage system for implementing the off-grid parallel startup method of the energy storage system involved above. Figure 6As shown, the energy storage system includes a plurality of parallel energy storage converters and a controller, the plurality of energy storage converters include a host and at least one slave, the controller includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores a computer program executable by the at least one processor, and the computer program is executed by the at least one processor so that the at least one processor can execute the off-grid parallel startup method of the energy storage system of the above embodiment, which is used to realize the synchronous parallel operation of the plurality of energy storage converters of the energy storage system in the off-grid mode.

[0093] In an exemplary embodiment, the controller may be a terminal, and its internal structure diagram may be as follows: Figure 7 As shown. The controller includes a processor, a memory, an input / output interface, a communication interface, a display unit and an input device. The processor, the memory and the input / output interface are connected through a system bus, and the communication interface, the display unit and the input device are connected to the system bus through the input / output interface. The processor of the controller is used to provide computing and control capabilities. The memory of the controller includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The input / output interface of the controller is used to exchange information between the processor and the external device. The communication interface of the controller is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be realized through WIFI, a mobile cellular network, NFC (near field communication) or other technologies. When the computer program is executed by the processor, the off-grid parallel startup method of the energy storage system is realized. The display unit of the controller is used to form a visually visible picture, which can be a display screen, a projection device or a virtual reality imaging device. The display screen can be a liquid crystal display screen or an electronic ink display screen, and the input device of the controller can be a touch layer covering the display screen, or a button, trackball or touchpad set on the controller housing, or an external keyboard, touchpad or mouse.

[0094] Those skilled in the art will understand that Figure 7 The structure shown in the figure is merely a block diagram of a partial structure related to the scheme of the present application, and does not constitute a limitation on the controller to which the scheme of the present application is applied. The specific controller may include more or fewer components than shown in the figure, or combine certain components, or have a different arrangement of components.

[0095] In an exemplary embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps of the off-grid parallel startup method of the energy storage system in the above embodiment are implemented.

[0096] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data permitted by the user or with full permission from all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0097] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic unit, a data processing logic unit, etc., but are not limited to this.

[0098] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0099] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. An off-grid parallel startup method for an energy storage system, used to realize synchronous parallel operation of multiple energy storage converters of the energy storage system in an off-grid mode, wherein the multiple energy storage converters include a master and at least one slave, characterized in that: The method comprises: After the host determines that the slave receives the start instruction, the host starts; The host performs DC side pre-charging, closes the AC relay after pre-charging is completed, establishes and outputs a black start voltage, and sends a voltage phase-locked synchronization start instruction to the slave; After receiving the voltage phase phase lock synchronization start instruction, the slave performs voltage and phase synchronization with the host with reference to the black start voltage, and sends a phase lock synchronization completion signal to the host after synchronization is completed; After the host receives the phase-locked synchronization completion signal and determines that the grid-connected slaves have all completed phase-locked synchronization, the host sends a voltage unification instruction to the slaves. Based on the voltage unification instruction, the host and the slaves are boosted from the black start voltage to the rated voltage to complete the parallel startup.

2. The off-grid parallel startup method of the energy storage system according to claim 1, characterized in that: During the startup process, the host obtains the current active power and the current reactive power of each of the energy storage converters connected to the grid, and obtains the average active power and the average reactive power of the energy storage converters connected to the grid; The host sends the active power average value and the reactive power average value to each of the slaves; The slave receives the active power mean value and the reactive power mean value sent by the host, and the slave adjusts power according to the active power mean value and the reactive power mean value.

3. The off-grid parallel startup method of the energy storage system according to claim 2, characterized in that: The host is started according to the voltage-frequency control mode, and the host controls the voltage and current through the outer voltage loop and the inner current loop; The outer voltage loop of the host adjusts the output voltage of the host according to a voltage set value and a voltage feedback signal, and the outer voltage loop outputs a current instruction to the inner current loop; The inner current loop adjusts the current of the host according to the current command and the current feedback signal.

4. The off-grid parallel startup method of the energy storage system according to claim 2, characterized in that: The voltage control of the slave adopts a power-current control mode, and the slave controls power and current through an outer power loop and an inner current loop to adjust the output voltage of the slave; The outer power loop adjusts the power of the slave according to a power given value and a power feedback signal, and the outer power loop outputs a current instruction to the inner current loop; The inner current loop of the slave adjusts the current of the slave according to the current command and the current feedback signal of the slave.

5. The off-grid parallel startup method of the energy storage system according to claim 4, characterized in that: While the slave performs voltage and phase synchronization, the slave uses the active power average value and the reactive power average value as the power set value of the outer power ring.

6. The off-grid parallel startup method of the energy storage system according to claim 1, characterized in that: When the host performs DC side pre-charging, the output voltage of the host is linearly ramped up from 0V to the black start voltage.

7. The off-grid parallel startup method of the energy storage system according to claim 6, characterized in that: The host adopts a linear ramp boost control so that the host and the slave are boosted from the black start voltage to the rated voltage in a linear ramp.

8. The off-grid parallel startup method of the energy storage system according to claim 7, characterized in that: The linear ramp voltage rise rate is less than 20V / ms.

9. An energy storage system, characterized in that: It comprises a plurality of parallel energy storage converters and a controller, wherein the plurality of energy storage converters comprise a host and at least one slave, and the controller comprises: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores a computer program executable by the at least one processor, and the computer program is executed by the at least one processor so that the at least one processor can execute the off-grid parallel startup method of the energy storage system as described in any one of claims 1 to 8, for realizing synchronous parallel operation of the plurality of energy storage converters of the energy storage system in an off-grid mode.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the off-grid parallel startup method of the energy storage system as described in any one of claims 1 to 8 is implemented.

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