High-voltage energy storage frequency conversion system and power supply switching method thereof

Abstract

The invention discloses a high-voltage energy storage frequency conversion system and a power supply switching method thereof, and the method comprises the steps: enabling an energy storage converter to collect a high-voltage signal of a power grid, obtaining a given power instruction of the system, monitoring the actual output power of the energy storage converter in real time, and calculating the impedance of the system; according to the obtained data, whether the device is in an island operation state is judged; and sending a corresponding signal to the high-voltage frequency converter according to the high-voltage signal of the power grid and the island judgment result, so that the high-voltage frequency converter controls the opening and closing of a contactor in a corresponding circuit, and switching from the power grid to the energy storage system to supply power to the load under the condition that the power grid is powered off, or switching from the energy storage system to the power grid to supply power to the load under the condition that the power grid is powered on. According to the scheme, the power failure of the current power supply can be recognized in time, smooth switching of power supply is achieved, no gap time exists between power supply switching, seamless switching is truly achieved, and therefore it can be guaranteed that an important load can operate uninterruptedly in the power supply switching process, and the reliability, stability and safety of operation of the whole system are improved.

Description

Technical Field

[0001] This application relates to the field of frequency conversion power supply, and in particular to a high-voltage energy storage frequency conversion system and its power supply switching method. Background Technology

[0002] With the continuous upgrading of electrification and automation capabilities, the power supply requirements for critical loads in power supply systems are becoming increasingly stringent. These systems need to be able to continuously supply power to the loads, even during power outages, ensuring prolonged operation. Furthermore, in many power supply systems, due to the large power of the motors, frequency converters are typically used for power supply.

[0003] For example, the loads of wind turbines in the coal industry are mostly electric motors with relatively large power. They generally require variable frequency speed control to reduce the impact on the power grid and prevent serious damage to other equipment.

[0004] Ventilation fans, as equipment used to ensure the safety of underground workers and the mine itself, have extremely high requirements for stable and continuous operation. This continuous operation also includes rapid switching in the event of a power outage. For example, when the mains power fails, power is restored by an emergency power source, or when power is restored, power is switched from the emergency power source to the mains power source. If the time spent during the power switching interval is too long, it can lead to a series of problems such as excessive methane levels.

[0005] Therefore, there is an urgent need for a power supply system that can operate at variable frequency and can achieve stable and rapid switching in the event of a power outage. Summary of the Invention

[0006] This application provides a high-voltage energy storage frequency converter system and its power supply switching method to solve the problem of the lack of a frequency converter power supply system that can achieve stable and rapid power supply switching when power is lost.

[0007] This application provides a power supply switching method for a high-voltage energy storage frequency converter system, including: The energy storage converter collects high-voltage signals from the power grid and obtains the system's given power command, while also monitoring its actual output power and calculating the system impedance in real time. Based on the acquired data, determine whether you are operating in an isolated state; Based on the high-voltage signal from the power grid and the islanding judgment result, a corresponding signal is sent to the high-voltage frequency converter, which controls the opening and closing of the contactor in the corresponding circuit. In the event of a power grid failure, the power is switched from the power grid to the energy storage system supplying power to the load, or in the event of a power grid restoration, the energy storage system switches to the power grid supplying power to the load.

[0008] In one example, before calculating the system impedance, the method further includes: when the power grid supplies power to the load, performing system impedance calibration for a preset time period to obtain a first calibration value, the first calibration value including the energy storage converter's own impedance, the load impedance, and the grid equivalent impedance; when the energy storage system supplies power to the load, performing system impedance calibration for a preset time period to obtain a second calibration value, the second calibration value including the energy storage converter's own impedance and the load impedance.

[0009] In one example, based on the acquired data, it is determined whether the energy storage converter is in an islanded operation state. Specifically, this includes: determining that the actual output power is consistent with the system's given power command, and determining that the system impedance is at or near the first calibration value. If so, it is determined that the energy storage converter is not in an islanded operation state.

[0010] In one example, based on the acquired data, it is determined whether the energy storage converter is in an islanded operation state. Specifically, this includes: determining that the difference between the actual output power and the system's given power command exceeds a preset threshold, and determining that the system impedance is a second calibration value or near the second calibration value.

[0011] In one example, based on the high-voltage grid signal and the islanding determination result, a corresponding signal is sent to the high-voltage frequency converter. Specifically, when the energy storage converter determines that it is in an islanded operation state, it sends a PCS islanding operation signal to the high-voltage frequency converter, causing the high-voltage frequency converter to disconnect the input contactor connected to the grid and switch to supplying power to the load by the energy storage system.

[0012] In one example, based on the high-voltage grid signal and the islanding determination result, a corresponding signal is sent to the high-voltage frequency converter. Specifically, when the energy storage system is supplying power to the load, and it is determined that the high-voltage grid signal has returned to normal, the energy storage converter performs a pre-synchronization operation and sends a pre-synchronization completion signal to the high-voltage frequency converter, causing the high-voltage frequency converter to control the input contactor connected to the grid to close, switching to power supply from the grid to the load, and terminating the islanding operation state of the energy storage converter.

[0013] In one example, the method further includes: when the energy storage converter determines that the high-voltage signal of the power grid is normal, the actual output power is consistent with the system's given power command, and determines that the system impedance is a first calibration value or near the first calibration value, and receives a valid frequency conversion operation signal from the high-voltage frequency converter, the energy storage converter enters a zero-power operation state.

[0014] In one example, the method further includes: the energy storage converter monitoring the battery power of the energy storage system; and automatically charging the energy storage system when the battery power is lower than a preset minimum limit.

[0015] In one example, the method further includes: when the energy storage system supplies power to the load, the energy storage converter sends a battery SOC status signal to the high-voltage frequency converter, causing the high-voltage frequency converter to execute maximum frequency adjustment logic based on the battery SOC status signal.

[0016] The high-voltage energy storage frequency converter system provided in this application embodiment operates based on the power supply switching method of the high-voltage energy storage frequency converter system described in any of the above claims. The system includes a voltage transformer, a high-voltage frequency converter, an energy storage converter, and an energy storage system. The first end of the phase-shifting transformer in the high-voltage frequency converter is connected to the power grid, the second end is connected to the power unit in the high-voltage frequency converter, and the third end is connected to the energy storage converter. One end of the voltage transformer is connected to the power grid via an input isolation switch, and the other end is connected to the phase-shifting transformer via a buffer circuit; The high-voltage frequency converter is also connected to a load; The energy storage converter is also connected to the energy storage system; When the power grid is supplying power normally, the load is driven to operate through the phase-shifting transformer and the power unit. When the power grid is cut off, the energy storage converter interacts with the high-voltage frequency converter by determining whether it is in an islanded operation state in order to control the energy storage system to drive the load to operate.

[0017] This application provides a high-voltage energy storage frequency conversion system and its power supply switching method, which can achieve the following beneficial effects: This application enables rapid judgment of the islanded operation status of the energy storage converter when the grid fails, and pre-synchronization operation of the energy storage converter when the grid is restored. It can promptly identify the power failure of the current power supply at the moment of power supply switching and achieve a smooth power supply switching, minimizing the gap time required for power supply switching and achieving seamless switching. This ensures that important loads can also operate without interruption during power supply switching, improving the reliability, stability and safety of the entire system.

[0018] Furthermore, by monitoring the battery's charge status, the system can automatically recharge the energy storage system when its charge is low, thus extending the system's lifespan.

[0019] In addition, this system simplifies the signal interaction between the high-voltage frequency converter and the energy storage converter, as well as the logic control of various operating conditions, thereby improving the stability and reliability of the system. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The accompanying drawings described herein are used to provide a further understanding of this application and constitute a part of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation of this application. In the accompanying drawings: Figure 1 This is a schematic diagram of the topology of a high-voltage energy storage frequency converter system provided in an embodiment of this application; Figure 2 A schematic diagram of the power supply switching method for a high-voltage energy storage frequency converter system provided in this application embodiment; Figure 3 A schematic diagram of the current output during power supply switching of the high-voltage energy storage frequency converter system provided in this application embodiment. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] Figure 1 A schematic diagram of the high-voltage energy storage frequency conversion system provided in the embodiments of this application.

[0023] like Figure 1 As shown, the system includes a high-voltage frequency converter, a power conversion system (PCS), and an energy storage system. The high-voltage frequency converter includes a phase-shifting transformer. The first end of the phase-shifting transformer is connected to the power grid via a high-voltage bus (such as a 6kV incoming line). The second end is connected to each power unit in the high-voltage frequency converter, and each power unit is then connected to the load. The third end is connected to the energy storage converter, which is also connected to the energy storage system.

[0024] When the power grid is supplying power normally, the load is driven to operate through the phase-shifting transformer and power unit; when the power grid is cut off, the PCS master controller of the energy storage converter determines whether it is in an islanded operation state and exchanges signals with the inverter master controller of the high-voltage frequency converter to control the energy storage system to drive the load to operate.

[0025] The grid power source can be a DC power source, an AC power source, a generator, etc., and the energy storage system can be an energy storage battery, depending on the specific conditions of the power supply site.

[0026] In one embodiment, the input terminal of the high-voltage frequency converter is equipped with an input isolation switch QS1 and a buffer circuit. The buffer circuit includes an input contactor KM1, a buffer contactor KM2, and a buffer resistor. The input isolation switch is used to separate the high-voltage busbar from the high-voltage frequency converter. The buffer contactors are connected to the buffer resistor, with one end of the input contactor connected to the buffer contactor and the other end connected to the buffer resistor. The resistance value of the buffer resistor can be determined based on factors such as the power grid supply and load in the power supply system.

[0027] During operation, the high-voltage frequency converter first controls the input isolating switch QS1 and the buffer contactor KM2 to close, so that the load is connected to the power grid through the line where the buffer resistor is located. After the operation is stable, the input contactor KM1 is closed, so that the load is directly connected to the power grid through the line where the input contactor KM1 is located.

[0028] By incorporating buffer contactors and buffer resistors as a transitional connection between the high-voltage frequency converter and the mains power supply, the current magnitude is limited during initial power startup and power outages followed by power restoration. This mitigates voltage fluctuations, ensuring stable output voltage from the frequency converter and a more stable energy exchange process. Particularly in high-power frequency converters, this protection mechanism safeguards capacitors and balances voltage, thereby enhancing equipment reliability and stability.

[0029] In addition, the system also includes voltage transformers (PTs). One end of the voltage transformer is connected to the power grid via an input isolating switch, and the other end is connected to a phase-shifting transformer via a buffer circuit. The voltage transformer is used to collect high-voltage signals from the power grid and transmit the data to the energy storage converter and high-voltage frequency converter, serving as the basis for their corresponding operations.

[0030] In one possible implementation, the high-voltage frequency converter has a power of 2000kW, a frequency range of 0-50Hz, and a voltage range of 0-6kV. The energy storage converter has a power of 1725kW, an AC rated voltage of 690V, and a DC voltage range of 1000-1500V. The energy storage system has a capacity of 600kWh and a voltage range of 1000-1500V. The voltage transformer has an accuracy class of 0.5 and a measurement range of 0-6kV. The system's main controller is a PLC-300, featuring data acquisition, logic control, and remote communication functions. The high-voltage frequency converter and the energy storage converter communicate via an RS485 interface at a communication rate of 38400bps.

[0031] In one embodiment, the phase-shifting transformer can be a multi-tap phase-shifting transformer to cope with changes in power supply voltage and maintain circuit voltage balance. The phase-shifting transformer includes a primary winding and a secondary winding. The primary winding is connected to the input contactor and the buffer resistor; the secondary winding is divided into two parts, one part as a phase-shifting multi-winding divided into three phases, with three power lines led out from each phase to connect to the corresponding power unit, and the other part as a conventional independent winding connected to the energy storage converter.

[0032] Each power unit module is identical, allowing for seamless replacement and providing electronic redundancy. The three corresponding power units are connected to the load motor via output contactor KM3 and output isolator QS2. By controlling the opening and closing of the output contactor and output isolator, the connection relationship between each power unit and the load can be determined. For example, if a power unit fails, the corresponding output contactor can be disconnected to cut off the connection between that power unit and the load, allowing other power units to supply power to the load.

[0033] In one embodiment, the energy storage converter includes an AC EMI filter, an AC filter, a DC / AC converter, a capacitor C, and a DC EMI filter connected in sequence, with the DC EMI filter connected to the energy storage system. When the grid fails, the DC power in the energy storage system can be converted into AC power by the components in the energy storage converter, and then supplied to the power unit through a phase-shifting transformer to drive the load.

[0034] The energy storage converter operates in grid-connected mode. In grid-connected mode, when the grid supplies power, active power can be directly supplied to charge and discharge the energy storage system and maintain the battery power. After the grid loses power, the energy storage system can drive the load to operate continuously.

[0035] During operation, current flows out through the high-voltage bus, passes through the input isolator QS1, input contactor KM1, buffer contactor KM2, and buffer resistor into the phase-shifting transformer, and then through the high-voltage frequency converter, output contactor KM3, and output isolator QS2 to connect to the load, driving the load to operate. When the power grid fails, the energy storage system supplies power, converting AC / DC to alternating current, which is then supplied to the load through the phase-shifting transformer, maintaining the load's continuous operation without interruption.

[0036] In summary, this system achieves smooth switching between energy storage power and grid power through signal interaction between the high-voltage frequency converter and the energy storage converter. It realizes power flow through the uncontrolled rectification of the high-voltage frequency converter, enabling stable operation of the load according to different operating conditions and improving the safety and reliability of important loads (such as motors in coal mines).

[0037] It should be noted that the topology proposed in this system does not limit the type of battery, the voltage level of the high-voltage frequency converter, or the type of power unit mentioned, as long as it can achieve the functions described in this system.

[0038] Based on the aforementioned high-voltage energy storage frequency converter system, this application proposes a power supply switching method for the high-voltage energy storage frequency converter system operating on this basis, such as... Figure 2 As shown.

[0039] Figure 2 This is a schematic flowchart of the power supply switching method for a high-voltage energy storage frequency converter system proposed in this application, which includes the following steps: S201: The energy storage converter collects high-voltage signals from the power grid, obtains the system's given power command, monitors its actual output power in real time, and calculates the system impedance.

[0040] The energy storage converter acquires frequency conversion operation signals through the external dry contacts of the high-voltage frequency converter and acquires the high-voltage signal of the power grid based on the PT signal. The high-voltage signal of the power grid can reflect the operating status of the power grid, and changes in the high-voltage signal of the power grid can be used to determine whether the power grid has lost power.

[0041] Furthermore, the energy storage converter also needs to obtain the power command given by the system and monitor its actual output power in real time. During operation, the energy storage converter outputs power based on the power command given by the system. However, in some cases, the actual output power of the energy storage converter may be inconsistent with the power command given by the system, which can also be used as a criterion for judging grid outages.

[0042] In addition, the energy storage converter also needs to calculate the system impedance. System impedance represents the impedance relationship between current and voltage in the entire system, and it is affected by the combined impedance of all devices in the system. The system impedance differs depending on the devices connected to the circuit during normal grid operation and during grid outages, thus it can be used to determine whether the grid has lost power. The system impedance can be obtained through the system impedance calculation algorithm built into the energy storage converter.

[0043] Because the system impedance may change when applied in different situations or adapted to different types of loads, the system impedance needs to be calibrated for the current application or the different types of loads it is adapted to before operation.

[0044] Specifically, system impedance calibration needs to be performed separately for different power supply conditions. When power is supplied from the grid to the load, system impedance calibration is performed for a preset time period to obtain a first calibration value. This first calibration value includes the energy storage converter's own impedance, the load impedance, and the grid's equivalent impedance. When power is supplied from the energy storage system to the load, system impedance calibration is performed for a preset time period to obtain a second calibration value. This second calibration value includes the energy storage converter's own impedance and the load impedance. The preset time period can be set as needed, such as 10 minutes.

[0045] S202: Based on the acquired data, determine whether it is in an isolated operation state.

[0046] Under normal grid operation, the energy storage converter operates in grid-connected mode, and is not in islanded operation. When the grid loses power, the high-voltage frequency converter disconnects from the circuit, and the energy storage converter then enters islanded operation. This islanded operation status of the energy storage converter can also be used to reflect whether the grid has lost power.

[0047] Specifically, under normal grid operation, the actual output power of the energy storage converter is basically consistent with the system's given power command, and the energy storage converter operates in grid-connected mode. Therefore, if the actual output power is consistent with the system's given power command, and the system impedance is determined to be at or near the first calibration value, it can be determined that the energy storage converter is not in islanded operation. Here, the consistency between the PCS's actual output power and the system's given power command does not require them to be exactly the same; a certain range of error is allowed. "Near the first calibration value" refers to a value within a preset fluctuation range that is close to the first calibration value, for example, a preset fluctuation range of -5% to 5%.

[0048] When the grid experiences a power outage, the actual output power of the energy storage converter deviates significantly from the system's given power command, and the system impedance changes. Therefore, if the difference between the actual output power and the system's given power command exceeds a preset threshold, and if the system impedance is at or near the second calibration value, leaving only its own impedance and the grid's equivalent impedance, then the energy storage converter is determined to be in islanded operation. Here, "near the second calibration value" refers to a value within a preset fluctuation range close to the second calibration value, for example, a preset fluctuation range of -5% to 5%.

[0049] In general, energy storage converters primarily determine whether they are in islanded operation by comprehensively considering two conditions: active power deviation and system impedance change. S203: Based on the high-voltage signal from the power grid and the islanding judgment result, send a corresponding signal to the high-voltage frequency converter, so that the high-voltage frequency converter controls the opening and closing of the contactor in the corresponding circuit, so that in the event of a power grid failure, the power supply is switched from the power grid to the energy storage system supplying power to the load, or in the event of a power grid restoration, the energy storage system switches to the power grid supplying power to the load.

[0050] Under different circumstances, such as when the power grid is interrupted or when power is restored, the high-voltage signal of the power grid will change accordingly, and the state of the energy storage converter will also change. Therefore, based on the changes in the high-voltage signal of the power grid and the state of the energy storage converter, timely signal exchange is required between the energy storage converter and the high-voltage frequency converter to switch power supplies.

[0051] In the embodiments of this application, the operation of the system under three different conditions will be described below.

[0052] First, during normal grid operation, the system operates at variable frequency. The high-voltage inverter can collect the grid high-voltage signal, detect changes in the grid high-voltage signal, and send a variable frequency operation signal. When the energy storage converter determines that the grid high-voltage signal is normal, the actual output power is consistent with the system's given power command, and the system impedance is at or near the first calibration value, and a valid variable frequency operation signal is received from the high-voltage inverter, the energy storage converter enters a zero-power operation state, i.e., a standby state. In this case, the actual output power of the energy storage converter is consistent with the system's given power command, and the energy storage converter continues to operate in grid-connected mode, supplying power to the load from the grid.

[0053] Specifically, when the high-voltage frequency converter detects that both the input and output isolating switches are closed, and there are no internal faults within the high-voltage frequency converter, it sends a closing permission signal. Furthermore, if the high-voltage frequency converter detects a normal high-voltage signal from the power grid, it will sequentially close the input and output contactors according to its normal operating mode to connect the power grid and the load, allowing the power grid to supply power to the load. It will also receive on-site start-up commands and frequency signals, operate at variable frequency, and send a variable frequency operation signal to the energy storage converter. If the energy storage converter detects both the high-voltage signal from the power grid and the variable frequency operation signal, it determines that the power grid supply is normal and remains in standby mode. The standard for a normal high-voltage signal can be set as needed, such as allowing slight fluctuations within a preset range.

[0054] Second, when the power grid fails, the high-voltage signal of the grid decreases, and the energy storage converter determines that it is in an islanded operation state. At this time, the energy storage converter sends a PCS islanded operation signal to the high-voltage frequency converter, causing the high-voltage frequency converter to disconnect the input contactor connected to the grid and switch to supplying power to the load by the energy storage system.

[0055] In this scenario, when the grid high-voltage signal decreases (e.g., to a preset threshold), the high-voltage inverter detects the high-voltage power failure and, assuming it is fault-free, executes a high-voltage power failure waiting state, continuously outputting an inverter operation signal. The waiting time is set and can be extended as needed. Since the PCS operates in grid-connected mode, it continues to operate with the load after a grid power failure. When the PCS detects the grid high-voltage signal decreasing to a preset threshold, it enters islanded operation mode and sends a PCS islanded operation signal to the high-voltage inverter. Upon detecting the decreased grid high-voltage signal and the PCS islanded operation signal, the high-voltage inverter disconnects the input contactor KM1, while the output contactor KM3 remains closed. The PCS then powers on offline, sending a battery state of charge (SOC) signal. Upon receiving the PCS offline operation signal, the high-voltage inverter operates normally, and the inverter's main controller executes the maximum frequency adjustment logic based on the SOC status signal transmitted by the PCS.

[0056] Third, when the energy storage system is supplying power to the load, the grid power supply is restored. At this time, once it is confirmed that the high-voltage signal of the grid has returned to normal, the energy storage converter performs a pre-synchronization operation and sends a pre-synchronization completion signal to the high-voltage frequency converter, causing the high-voltage frequency converter to close the input contactor connected to the grid, switching to grid power supply to the load. At the same time, the islanded operation state of the energy storage converter will also terminate.

[0057] In this situation, once the high-voltage signal of the power grid is restored, the PCS needs to be shut down and connected to the grid, so that the load motor, which was powered by the energy storage system, can switch back to grid-driven operation.

[0058] Specifically, when the PCS detects that the high-voltage grid has recovered and the duration is sufficient, meeting the switching conditions, it immediately begins the PCS pre-synchronization operation. It adjusts the amplitude and phase of the PCS AC voltage to quickly synchronize with the grid and continuously tracks it, informing the high-voltage inverter to prepare for grid switching. After the PCS pre-synchronization is completed (i.e., phase-locked loop and voltage amplitude synchronization are successful), it sends a PCS pre-synchronization completion signal. When the high-voltage inverter detects that the high-voltage grid has recovered and the duration is sufficient, meeting the switching conditions, and receives the PCS pre-synchronization completion signal, and its self-test is fault-free, it controls the input contactor KM1 to close, while the buffer contactor remains stationary to perform the power switching. The power switching is then complete. The maximum frequency set by the inverter's main control is executed according to the value set by the HMI. The judgment condition for the completion of phase-locked loop and voltage amplitude synchronization can be that the phase difference and voltage difference are less than preset thresholds.

[0059] In one embodiment, the main controller of the energy storage converter can monitor the battery power of the energy storage system, such as collecting battery power information at preset time intervals. When the battery power is lower than a preset minimum limit, it automatically charges the energy storage system to ensure that the energy storage system can always maintain a healthy power level, facilitating power supply to the load when the grid fails.

[0060] In this embodiment, the high-voltage frequency converter and the energy storage system are connected through a phase-shifting transformer. When the high-voltage power of the bus is normal, the power grid drives the frequency converter to operate normally through the phase-shifting transformer, and the energy storage converter is in standby mode (i.e., non-islanded operation). When the high-voltage power of the bus is lost, the energy storage converter operates off-grid and is in islanded operation mode. The system then switches to the energy storage system driving the frequency converter to operate normally through the phase-shifting transformer. This ensures the continuous operation of the load and enables the stable operation of loads such as wind turbines even if the power grid fails, achieving uninterrupted operation of wind power during power outages.

[0061] Furthermore, by judging whether it is in an islanded operation state and performing pre-synchronization operations, the energy storage converter can promptly identify the power failure of the current power supply during power supply switching moments such as when the grid is interrupted or restored, and achieve a smooth power supply switching, minimizing the gap time required for power supply switching and achieving seamless switching. This improves the reliability, stability and safety of the entire system operation.

[0062] In addition, this system simplifies the signal interaction between the high-voltage frequency converter and the energy storage converter, as well as the logic control of various operating conditions, thereby improving the stability and reliability of the system.

[0063] In one embodiment, the signal interaction between the high-voltage frequency converter and the energy storage converter can be understood through Table 1. The first column represents the relevant signals, the second and third columns represent the signal sender and receiver, respectively, and the fourth column provides explanations and descriptions of the signals.

[0064] Table 1 Figure 3 This is a schematic diagram of the current output during power supply switching of the high-voltage energy storage frequency converter system provided in this application embodiment. As shown in the figure, the output current of the frequency converter has almost no fluctuation, indicating that the important load (such as the main ventilation fan) is running continuously. The high-voltage side grid input current suddenly increases from 0, indicating that after the grid power is restored, when the input contactor (i.e., the grid connection switch) KM1 is closed, the load power is switched from being borne by the energy storage system to being borne by the grid.

[0065] It should be noted that this high-voltage energy storage inverter signal interaction method is based on a system consisting of a high-voltage inverter, an energy storage converter, and an energy storage system. The high-voltage inverter and the energy storage power supply are connected using a phase-shifting transformer to achieve continuous power supply. Even if other additional functions are added to the system or the main circuit of the high-voltage inverter is changed, the signal interaction control method between the high-voltage inverter and the energy storage converter remains unchanged. This application only uses the one-to-one automatic buffered main circuit of the high-voltage inverter as an example for illustration and does not limit other circuit topologies that can achieve the functions described in this application.

[0066] The various embodiments in this application are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0067] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0068] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A power supply switching method for a high-voltage energy storage frequency conversion system, characterized in that, The method includes: The energy storage converter collects high-voltage signals from the power grid and obtains the system's given power command, while also monitoring its actual output power and calculating the system impedance in real time. Based on the acquired data, determine whether you are operating in an isolated state; Based on the high-voltage signal from the power grid and the islanding judgment result, a corresponding signal is sent to the high-voltage frequency converter, which controls the opening and closing of the contactor in the corresponding circuit. In the event of a power grid failure, the power is switched from the power grid to the energy storage system supplying power to the load, or in the event of a power grid restoration, the energy storage system switches to the power grid supplying power to the load.

2. The power supply switching method for a high-voltage energy storage frequency conversion system according to claim 1, characterized in that, Before calculating the system impedance, the method further includes: When power is supplied to the load from the grid, the system impedance is calibrated for a preset time period to obtain a first calibration value. The first calibration value includes the impedance of the energy storage converter itself, the load impedance, and the grid equivalent impedance. When the energy storage system supplies power to the load, the system impedance is calibrated for a preset time period to obtain a second calibration value, which includes the impedance of the energy storage converter itself and the load impedance.

3. The power supply switching method for a high-voltage energy storage frequency conversion system according to claim 2, characterized in that, Based on the acquired data, determine whether you are operating in an isolated state, specifically including: If the actual output power is consistent with the system's given power command, and the system impedance is determined to be at or near the first calibration value, then it is determined that the energy storage converter is not in an islanded operation state.

4. The power supply switching method for a high-voltage energy storage frequency conversion system according to claim 2, characterized in that, Based on the acquired data, determine whether you are operating in an isolated state, specifically including: If the difference between the actual output power and the system's given power command exceeds a preset threshold, and if the system impedance is determined to be at or near the second calibration value, then the energy storage converter is determined to be in an islanded operation state.

5. The power supply switching method for a high-voltage energy storage frequency conversion system according to claim 1, characterized in that, Based on the high-voltage grid signal and the islanding determination result, a corresponding signal is sent to the high-voltage frequency converter, specifically including: When the energy storage converter determines that it is in an islanded operation state, it sends a PCS islanded operation signal to the high-voltage frequency converter, causing the high-voltage frequency converter to disconnect the input contactor connected to the power grid and switch to supplying power to the load by the energy storage system.

6. The power supply switching method for a high-voltage energy storage frequency conversion system according to claim 1, characterized in that, Based on the high-voltage grid signal and the islanding determination result, a corresponding signal is sent to the high-voltage frequency converter, specifically including: When the energy storage system supplies power to the load, and it is determined that the high-voltage signal of the power grid has returned to normal, the energy storage converter performs a pre-synchronization operation and sends a pre-synchronization completion signal to the high-voltage frequency converter, causing the high-voltage frequency converter to control the input contactor connected to the power grid to close, switching to power supply from the power grid to the load, and terminating the islanded operation state of the energy storage converter.

7. The power supply switching method for a high-voltage energy storage frequency conversion system according to claim 1, characterized in that, The method further includes: When the energy storage converter determines that the high-voltage signal of the power grid is normal, the actual output power is consistent with the system's given power command, and the system impedance is at or near the first calibration value, and receives a valid frequency conversion operation signal from the high-voltage frequency converter, the energy storage converter enters a zero-power operation state.

8. The power supply switching method for a high-voltage energy storage frequency conversion system according to claim 1, characterized in that, The method further includes: The energy storage converter monitors the battery power of the energy storage system; When the battery charge falls below a preset minimum limit, the energy storage system is automatically charged.

9. The power supply switching method for a high-voltage energy storage frequency conversion system according to claim 1, characterized in that, The method further includes: When the energy storage system supplies power to the load, the energy storage converter sends a battery SOC status signal to the high-voltage frequency converter, causing the high-voltage frequency converter to execute maximum frequency adjustment logic based on the battery SOC status signal.

10. A high-voltage energy storage frequency converter system, operating based on the power supply switching method of the high-voltage energy storage frequency converter system according to any one of claims 1 to 9, characterized in that, The system includes a voltage transformer, a high-voltage frequency converter, an energy storage converter, and an energy storage system; The first end of the phase-shifting transformer in the high-voltage frequency converter is connected to the power grid, the second end is connected to the power unit in the high-voltage frequency converter, and the third end is connected to the energy storage converter. One end of the voltage transformer is connected to the power grid via an input isolation switch, and the other end is connected to the phase-shifting transformer via a buffer circuit; The high-voltage frequency converter is also connected to a load; The energy storage converter is also connected to the energy storage system; When the power grid is supplying power normally, the load is driven to operate through the phase-shifting transformer and the power unit. When the power grid is cut off, the energy storage converter interacts with the high-voltage frequency converter by determining whether it is in an islanded operation state in order to control the energy storage system to drive the load to operate.

Images