Grid-side relay topology system in energy storage inverter, self-checking method and energy control strategy

Abstract

The invention discloses a network side relay topology system in an energy storage inverter in the technical field of power electronics and electricians, which comprises an energy storage inverter main circuit and a control system, and is characterized in that the energy storage inverter main circuit comprises a network side relay topology; the invention discloses a self-checking method for a network side relay topology in an energy storage inverter. The self-checking method comprises the following steps: S1, a relay RY2 and a relay RY3 are combined to detect whether a short-circuit fault and an open-circuit fault occur in a contact of the relay RY2 and the relay RY3; s2, a relay RY1 detects whether a short-circuit fault and an open-circuit fault occur in a contact of the relay RY1; according to the invention, the power failure fault of the commercial power can be rapidly detected, so that the switching time from grid connection to grid disconnection is greatly shortened, and the backup load works stably; the system cost is reduced, additional fault points possibly introduced due to the addition of hardware modules are avoided, and the reliability and engineering applicability of the system are improved; through optimization of a digital signal processing technology, optimal utilization of hardware resources is realized while the detection precision is ensured.

Description

Technical Field

[0001] This invention relates to the fields of power electronics and electrical engineering, and particularly to the grid-side relay topology system, self-testing method, and energy control strategy in energy storage inverters. Background Technology

[0002] Photovoltaic energy storage inverter systems combine photovoltaic power generation and UPS functions. On the AC grid side, they support both grid-connected and off-grid operation modes, with switching between these modes mostly achieved through relay switching for small to medium power applications. In grid-connected mode, the system can control the switching of grid-side relays to ensure photovoltaic energy feeds to the grid and that the grid prioritizes power supply to backup loads. When a grid fault causes a power outage, the system must enter off-grid mode, controlling the relay network to disconnect the inverter in the photovoltaic energy storage inverter system from the grid, allowing the inverter to provide uninterrupted power to backup loads. According to standards such as TUV and CGC, the relay network must have hardware self-testing capabilities before the photovoltaic energy storage inverter system can operate normally. This means that before the photovoltaic energy storage inverter system operates normally, the relay coil driving capability and whether the contacts can operate normally (closing / releasing) must be verified to determine if there are any open-circuit or short-circuit faults in the relays.

[0003] Although grid-side inverters in current photovoltaic (PV) energy storage grid-connected systems have mature self-testing schemes, the complexity of relay topologies reduces the reliability of PV energy storage systems and leads to cumbersome control logic. More importantly, the existing grid-side relay network has become a bottleneck for grid-to-off-grid switching time, especially for critical loads with extremely high uninterrupted power supply requirements, making it difficult to achieve short-time switching from grid to off-grid. To shorten the switching time of PV energy storage inverter systems from grid to off-grid during grid outages, the current solution is to connect thyristors in parallel to the contacts of the load-side relays in the grid-side relay network. This effectively reduces the duration of uninterrupted power supply to the backup load during grid outages, but it increases system cost and reduces system reliability, thus significantly reducing cost-effectiveness. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a grid-side relay topology system, self-testing method, and energy control strategy for energy storage inverters.

[0005] The objective of this invention is achieved as follows: a grid-side relay topology system in an energy storage inverter, comprising an energy storage inverter main circuit and a control system, wherein the energy storage inverter main circuit includes a grid-side relay topology, and the control system is electrically connected to the energy storage inverter main circuit;

[0006] The network-side relay topology consists of relays RY1, RY2, and RY3. Relays RY1, RY2, and RY3 are divided into two combinations. The first combination module is composed of relays RY2 and RY3, and the second combination module is composed of relays RY1.

[0007] The normally open contacts of relays RY2 and RY3 in the first combination module are connected in series to form a first bridge arm. One end of the first bridge arm is connected to the grid terminal, and the other end of the first bridge arm is connected to the AC bus. A backup load is electrically connected to the AC bus. The relay RY1 in the second combination module forms a second bridge arm. One end of the second bridge arm is connected to the AC output terminal of the inverter, and the other end of the second bridge arm is connected to the AC bus.

[0008] Furthermore, the other end of the inverter is connected to a high-voltage side DC bus, and the other side of the high-voltage side DC bus is electrically connected to an MPPT controller and a battery charging and discharging circuit, respectively. A photovoltaic module is electrically connected to the MPPT controller, and an energy storage battery is electrically connected to the battery charging and discharging circuit.

[0009] Furthermore, the control system includes a signal acquisition and fault detection system, a drive controller, and a TMS320F28035 controller. The signal acquisition and fault detection system is used to acquire voltage signals from the grid terminal and the energy storage battery, and to perform fault analysis and processing. The TMS320F28035 controller is electrically connected to the signal acquisition and fault detection system via AD sampling, and is used to perform AD signal sampling on the signal acquisition and fault detection system.

[0010] Furthermore, the TMS320F28035 controller is configured with GPIO22, GPIO41, and GPIO44 as output I / O ports. The TMS320F28035 controller transmits the acquired AD signal through the GPIO22, GPIO41, and GPIO44 output I / O ports to the coil and driver of relay RY1, the coil and driver of relay RY2, and the coil and driver of relay RY3. The driver is used to power the coils of relays RY1, RY2, and RY3, thereby controlling the closing of the normally open contacts of relays RY1, RY2, and RY3.

[0011] The self-testing method of the grid-side relay topology in the energy storage inverter is as follows: when the mains power fails, the combined detection of the first combined module and the second combined module is used. When the grid is normal, the grid-side relay topology needs to be self-tested before the main circuit of the energy storage inverter is running normally. At this time, the inverter in the main circuit of the energy storage inverter does not work.

[0012] Includes the following steps:

[0013] S1. The combination of relays RY2 and RY3 is used to detect whether a short circuit fault or an open circuit fault has occurred at their contacts;

[0014] S2. Relay RY1 is used to detect whether a short circuit or open circuit fault has occurred at its contacts.

[0015] Furthermore, the specific operation procedure for detecting whether the contacts of relays RY2 and RY3 in S1 have short-circuit or open-circuit faults is as follows:

[0016] During the initialization phase, the coils of relays RY2 and RY3 are de-energized, and the contacts are in the released state. Subsequently, the response characteristics of contact closing and releasing are verified by alternately driving relay RY2 to be energized, relay RY3 to be de-energized, and both coils to be energized and de-energized simultaneously. During the delay period from DelayTime1 to DelayTime4, the difference between the effective value of the grid voltage and the effective value of the backup load voltage is continuously monitored. If the difference approaches 0, it is determined to be a short circuit fault. If the difference is stable and close to the grid voltage, it is determined to be an open circuit fault.

[0017] Furthermore, the specific steps for the relay RY1 in S2 to detect whether its contacts have short-circuit or open-circuit faults are as follows:

[0018] With relay RY2 or relay RY3 closed, the coil of relay RY1 is first de-energized to release its contacts. Then, during the DelayTime3 phase, the coil of relay RY1 is energized, causing the normally open contacts of both relay RY1 and relay RY2 to close. During the DelayTime4 phase, the effective value difference between the grid voltage and the inverter output voltage is continuously monitored. If the difference is close to 0, a short circuit fault is determined for relay RY1; otherwise, an open circuit fault detection is initiated. If the difference continues to be close to the effective value of the grid voltage, an open circuit fault is determined.

[0019] Furthermore, the determination of the power grid failure is as follows:

[0020] A voltage setting value for grid power failure is set, and a grid power failure filtering window is given. If the grid voltage is lower than the voltage setting value for grid power failure, corresponding to a fixed number of low-voltage counting points, and the number of low-voltage counting points lower than the voltage setting value for grid power failure counted in the grid power failure filtering window is greater than the fixed number of low-voltage counting points, it is determined that a grid power failure has occurred at this time.

[0021] If the number of low-voltage counting points counted in the power grid failure filtering window that is lower than the set value of the power grid voltage failure is less than the fixed number of low-voltage counting points, it is determined that the power grid is normal at this time, that is, no power failure has occurred.

[0022] The method for rapid detection of mains power failure in the grid-side relay topology of the main circuit of the energy storage inverter can quickly identify the mains voltage failure when a mains power failure occurs, and send a control command to the grid-side relay topology to quickly disconnect relays RY2 and RY3 in the grid-side relay topology. At the same time, it allows the inverter to switch from current-type control mode to voltage-type control mode to provide uninterrupted energy for the backup load.

[0023] Energy control strategy of grid-side relay topology in energy storage inverter: During operation of the main circuit of energy storage inverter, when there is no grid fault, but a grid fault occurs:

[0024] When a grid fault occurs, relays RY2 and RY3 are disconnected, and the inverter switches from current-mode control to voltage-mode control to provide uninterrupted energy to the backup load.

[0025] When the power grid returns to normal, the inverter, after achieving phase amplitude tracking of the power grid, disconnects relay RY1 and simultaneously closes relays RY2 and RY3, so that the power grid prioritizes power supply to the backup load.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] The grid-side relay topology, self-testing method, and energy control strategy of the energy storage inverter of this invention not only support both grid-connected and off-grid operation modes on the AC grid side, but also use fewer relays compared to traditional grid-side relay networks, which helps to improve system power density, reduce costs, and improve reliability. The reduction in the number of relays in the relay topology makes the self-testing process relatively simple, and the rapid detection method for mains power failure can quickly detect mains power failure, thereby greatly shortening the switching time from grid-connected to off-grid and ensuring stable operation of backup loads.

[0028] The method of this invention makes full use of the existing voltage sampling signal in the photovoltaic energy storage system and realizes rapid detection of grid power outage faults through software algorithms without the need for additional hardware detection circuits. The design method based on existing signal processing not only reduces system costs but also avoids additional fault points that may be introduced by adding hardware modules, significantly improving the reliability and engineering applicability of the system. Through the optimization of digital signal processing technology, the optimal utilization of hardware resources is achieved while ensuring detection accuracy, resulting in high cost-effectiveness and suitability for engineering applications.

[0029] The self-testing method for the disclosed relay topology can be applied not only to photovoltaic energy storage inverters but also to wind power energy storage devices, effectively improving the adaptability of the method. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the network-side relay topology of the present invention;

[0032] Figure 2 This is a schematic diagram illustrating the implementation of the present invention in the main circuit of an energy storage inverter;

[0033] Figure 3 This is a flowchart illustrating the program initialization process for implementing this invention.

[0034] Figure 4 The flowchart of the self-test algorithm program for relays RY2 and RY3 of the present invention is shown below;

[0035] Figure 5 This is a flowchart of the relay RY1 self-test algorithm program of the present invention;

[0036] Figure 6 This is a schematic diagram of the power grid failure detection principle of the present invention;

[0037] Figure 7 This is a flowchart of the power grid failure detection algorithm of the present invention;

[0038] Figure 8 This is a flowchart of the on-grid / off-grid handover algorithm of the present invention;

[0039] Figure 9 This is a schematic diagram illustrating the composition principle of an embodiment of the present invention;

[0040] Figure 10The waveforms shown are experimental waveforms for switching from grid-connected to off-grid operation, as described in an embodiment of the present invention.

[0041] in: Figure 1 Symbol names in:

[0042]

[0043] Figure 2 Symbol names in:

[0044]

[0045] Figure 4 Symbol names in:

[0046]

[0047] Figure 5 Symbol names in:

[0048]

[0049] Other symbols are the same Figure 4 ;

[0050] Figure 7 Symbol names in:

[0051]

[0052] Figure 8 Symbol names in:

[0053]

[0054] Figure 9 Symbol names in:

[0055]

[0056] Other symbols are the same Figure 2 ;

[0057] Figure 10 Symbol names in:

[0058] . Detailed Implementation

[0059] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] like Figures 1 to 10 The grid-side relay topology system of the energy storage inverter shown includes an energy storage inverter main circuit and a control system. The energy storage inverter main circuit includes a grid-side relay topology, and the control system is electrically connected to the energy storage inverter main circuit.

[0061] The network-side relay topology consists of relays RY1, RY2, and RY3. Each of relays RY1, RY2, and RY3 has two sets of normally open contacts. Relays RY1, RY2, and RY3 are divided into two combinations. The first combination module is composed of relays RY2 and RY3, and the second combination module is composed of relays RY1.

[0062] The normally open contacts of relays RY2 and RY3 in the first combination module are connected in series to form a first bridge arm. One end of the first bridge arm is connected to the grid terminal, and the other end of the first bridge arm is connected to the AC bus. A backup load is electrically connected to the AC bus. The relay RY1 in the second combination module forms a second bridge arm. One end of the second bridge arm is connected to the AC output terminal of the inverter, and the other end of the second bridge arm is connected to the AC bus.

[0063] In the first bridge arm, the normally open contacts of relays RY2 and RY3 are connected in series to form an electrical channel between the AC side bus and the grid connection terminal in the main circuit of the energy storage inverter; in the second bridge arm, the normally open contact of relay RY1 forms an electrical channel between the AC output terminal of the inverter and the AC side bus in the main circuit of the energy storage inverter.

[0064] The AC busbar is directly connected to the backup load, allowing the backup load to be powered by either the grid or the inverter in the main circuit of the energy storage inverter via the grid-side relay topology. Specifically, it obtains power from the grid through the first arm of the grid-side relay topology or from the inverter in the main circuit of the energy storage inverter through the second arm of the grid-side relay topology. When the grid is present, the grid supplies power to the backup load, while when the grid fails, the energy storage inverter supplies power to the backup load, thus achieving uninterrupted power supply to the backup load.

[0065] In this embodiment, preferably, the other end of the inverter is connected to a high-voltage side DC bus, and the other side of the high-voltage side DC bus is electrically connected to an MPPT controller and a battery charging and discharging circuit, respectively. A photovoltaic module is electrically connected to the MPPT controller, and an energy storage battery is electrically connected to the battery charging and discharging circuit.

[0066] It should be noted that by integrating the inverter with the high-voltage side DC bus and combining the collaborative design of the MPPT controller and battery charging and discharging circuit, efficient energy management of the photovoltaic system and energy storage device is achieved; the MPPT controller tracks the maximum power point of the photovoltaic module in real time, significantly improving the light energy conversion efficiency and reducing energy loss; and seamless connection of photovoltaic power generation, energy storage charging and discharging and grid-connected output is achieved, enhancing the stability and economy of the system.

[0067] In this embodiment, preferably, the control system includes a signal acquisition and fault detection system, a drive controller, and a TMS320F28035 controller. The signal acquisition and fault detection system is used to acquire the voltage signals of the grid terminal and the energy storage battery, and to perform fault analysis and processing. The TMS320F28035 controller is electrically connected to the signal acquisition and fault detection system through AD sampling, and is used to realize AD signal sampling of the signal acquisition and fault detection system.

[0068] It should be noted that the voltage of the energy storage battery in the main circuit of the energy storage inverter and the voltage at the grid end are monitored through signal acquisition and fault detection. The voltage signals are processed to facilitate the analysis of the voltage signal values. The TMS320F28035 controller acquires the voltage signals, which enables the TMS320F28035 controller to perform fault analysis and processing based on the voltage signals, facilitating subsequent control and adjustment.

[0069] In this embodiment, preferably, the TMS320F28035 controller is configured with GPIO22, GPIO41, and GPIO44 as output I / O ports. The TMS320F28035 controller transmits the acquired AD signal to the coil and driver of relay RY1, the coil and driver of relay RY2, and the coil and driver of relay RY3 through the output I / O ports of GPIO22, GPIO41, and GPIO44. The driver is used to power the coils of relays RY1, RY2, and RY3, thereby controlling the closing of the normally open contacts of relays RY1, RY2, and RY3.

[0070] It should be noted that the coil settings enable the analysis and processing of short circuits and open circuits for relays RY1, RY2, and RY3, and the drive controls and adjusts the normally open contacts of relays RY1, RY2, and RY3 to make contact.

[0071] The self-testing method of the grid-side relay topology in the energy storage inverter is as follows: when the mains power fails, the combined detection of the first combined module and the second combined module is used. When the grid is normal, the grid-side relay topology needs to be self-tested before the main circuit of the energy storage inverter is running normally. At this time, the inverter in the main circuit of the energy storage inverter does not work.

[0072] Includes the following steps:

[0073] S1. The combination of relays RY2 and RY3 is used to detect whether a short circuit fault or an open circuit fault has occurred at their contacts;

[0074] S2. The relay RY1 is used to detect whether a short circuit fault or an open circuit fault has occurred at its contacts;

[0075] It should be noted that the self-testing method for the grid-side relay topology, designed to detect faults in the hardware circuitry of the grid-side relay topology within the energy storage inverter system, primarily diagnoses short-circuit and open-circuit faults in the relay contacts. This process is performed before the energy storage inverter is connected to the grid for normal operation. Specifically, if a short-circuit or open-circuit fault exists in the grid-side relay topology, the energy storage inverter is not allowed to enter normal operating mode, thus ensuring the safety of the energy storage inverter and the reliable operation of the grid. The logic involved in the grid-side relay topology, self-testing method, and energy control strategy in the energy storage inverter considers the functional requirements of both grid-connected and off-grid operation modes. In both operating modes, the energy storage inverter can supply power to backup loads. To achieve seamless integration between the state of the grid-side relay topology after self-testing and the normal operating state entered by the energy storage inverter, a self-testing method for the grid-side relay topology is proposed.

[0076] In this embodiment, preferably, the specific operation procedure for detecting whether the contacts of relays RY2 and RY3 in S1 have short-circuit faults or open-circuit faults is as follows:

[0077] During the initialization phase, the coils of relays RY2 and RY3 are de-energized, and the contacts are in the released state. Subsequently, the response characteristics of contact closing and releasing are verified by alternately driving relay RY2 to be energized, relay RY3 to be de-energized, and both coils to be energized and de-energized simultaneously. During the delay period from DelayTime1 to DelayTime4, the difference between the effective value of the mains voltage and the effective value of the backup load voltage is continuously monitored. If the difference approaches 0, it is determined to be a short circuit fault. If the difference is stable and close to the mains voltage, it is determined to be an open circuit fault.

[0078] The specific steps are as follows:

[0079] After the main circuit of the energy storage inverter is connected to the grid, the initialization process causes the coils of all relays RY1, RY2 and RY3 in the grid-side relay topology to be de-energized, thereby causing the normally open contacts of relays RY1, RY2 and RY3 to be in the released state.

[0080] Then, by driving the coil of relay RY2 to be energized and the coil of relay RY3 to be de-energized, the drive can control the normally open contact of relay RY2 to close and the normally open contact of relay RY3 to release; after a period of time until DelayTime1, the coils of relays RY2 and RY3 are de-energized, thereby causing the normally open contacts of relays RY2 and RY3 to release.

[0081] After a further extension until DelayTime2, the coil of relay RY2 is de-energized and the coil of relay RY3 is energized, thereby causing the normally open contact of relay RY2 to release and the normally open contact of relay RY3 to close; after a further extension until DelayTime3, the coils of both relay RY2 and relay RY3 are energized, thereby causing the normally open contacts of both relay RY2 and relay RY3 to close, and then the extension continues until DelayTime4;

[0082] The terminal voltage v of the backup load is continuously monitored during the DelayTime3 time period. ac and grid voltage v g and the effective value of the grid voltage v grms The effective value of the terminal voltage v of the backup load acrms If the difference is small and close to 0, it indicates that the contacts of relays RY2 and RY3 have a short circuit fault; if the difference is large and close to the effective value of the mains voltage, it indicates that the contacts of relays RY2 and RY3 have a short circuit fault. grms This indicates that there is no short circuit fault at the contacts of relays RY2 and RY3;

[0083] If a short circuit fault occurs at the contact of relay RY2 or relay RY3, a short circuit fault report is issued for relay RY2 or relay RY3; if no short circuit fault occurs at the contact of relay RY2 and relay RY3, an open circuit fault detection is performed on the contact of relay RY2 and relay RY3.

[0084] The terminal voltage v of the backup load is continuously monitored after the DelayTime4 time period. ac and grid voltage v g The effective value of the grid voltage v grmsThe effective value of the terminal voltage v of the backup load acrms The difference is calculated, and if the difference remains large and close to the effective value of the mains voltage within the DelayTime5 period, it indicates that the contacts of relays RY2 and RY3 have an open circuit fault; if the difference is small and close to 0, it indicates that the contacts of relays RY2 and RY3 have not had an open circuit fault.

[0085] If an open circuit fault occurs at the contact of relay RY2 or relay RY3, an open circuit fault report is issued for relay RY2 and relay RY3; if no open circuit fault occurs at the contact of relay RY2 and relay RY3, S1 ends and S2 is implemented, at which point the power grid is supplying power to the backup load.

[0086] It should be noted that the rapid detection method for mains power outage faults in the grid-side relay topology of the energy storage inverter can quickly identify grid anomalies when a mains power outage occurs, thereby issuing control commands to the grid-side relay topology. The energy control strategy of the grid-side relay topology in the energy storage inverter enables the inverter (bidirectional AC / DC) to provide energy to backup loads by controlling the grid-side relay topology in the energy storage inverter when a mains power outage occurs; when the mains power is restored, the grid-side relay topology in the energy storage inverter can be controlled to prioritize the mains power to provide energy to backup loads.

[0087] In this embodiment, preferably, the specific steps for the relay RY1 in S2 to detect whether its contacts have short-circuit or open-circuit faults are as follows:

[0088] With relay RY2 or RY3 closed, the coil of relay RY1 is first de-energized to release its contacts. Then, during the DelayTime3 phase, the coil of relay RY1 is energized, causing the normally open contacts of both relay RY1 and relay RY2 to close. During the DelayTime4 phase, the effective value difference between the grid voltage and the inverter output voltage is continuously monitored. If the difference is close to 0, a short circuit fault is determined in relay RY1; otherwise, an open circuit fault detection is initiated. If the difference remains close to the effective value of the grid voltage, an open circuit fault is determined.

[0089] The specific steps are as follows:

[0090] When the coil of relay RY2 or relay RY3 is energized, the normally open contact of relay RY2 or relay RY3 is closed; at this time, the coil of relay RY1 is de-energized, the normally open contact of relay RY1 is released, and after a period of time until DelayTime3, the coil of relay RY1 is energized, so that the normally open contacts of relay RY1 and relay RY2 are closed; and then the period of time is extended again until DelayTime4.

[0091] Continuously monitor the grid voltage v during the DelayTime3 time period. g and inverter output voltage v inv and the effective value of the grid voltage v grms With the effective value of the inverter output voltage v invrms If the difference is small and close to 0, it indicates that the contacts of relay RY1 have a short circuit fault; if the difference is large and close to the effective value of the mains voltage, it indicates that the contacts of relay RY1 have a short circuit fault. grms This indicates that the contacts of the relay RY1 have not experienced a short circuit fault;

[0092] If a short circuit fault occurs at the contact of relay RY1, a short circuit fault report for relay RY1 is issued; if no short circuit fault occurs at the contact of relay RY1, an open circuit fault detection is performed on the contact of relay RY1.

[0093] Continuously monitor the grid voltage v after the DelayTime4 time period. g and inverter output voltage v inv The effective value of the grid voltage v grms With the effective value of the inverter output voltage v invrms Calculate the difference, and if the difference remains large and close to the effective value of the grid voltage v for up to DelayTime5, then... grms If the difference is small and close to 0, it indicates that the contacts of relay RY1 have an open circuit fault; if the difference is small and close to 0, it indicates that the contacts of relay RY1 have not had an open circuit fault.

[0094] When an open circuit fault occurs in the contact of relay RY1, an open circuit fault of relay RY1 is reported; when no open circuit fault occurs in the contact of relay RY1, S2 ends and the flag indicating that all relays have been tested is set. At this time, if the main circuit of the energy storage inverter has been connected to the photovoltaic module, it can enter the grid-connected power generation start-up state if there are no other faults.

[0095] It should be noted that, firstly, a self-test was performed on the relay group between the grid connection terminal and the AC bus. If there were no hardware short-circuit or open-circuit faults, the normally open contacts of relays RY2 and RY3 in this group would close, thus achieving electrical connection between the grid and the backup load, meaning the grid would supply power to the backup load, thereby ensuring that the backup load is energized. Secondly, a self-test was performed on the relay between the inverter's AC output terminal and the AC bus in the energy storage inverter system. If there were no hardware short-circuit or open-circuit faults, the contact of relay RY1 would close, indicating that the system was in grid-connected state. Therefore, when there are photovoltaic modules in the system and no other faults, it can directly enter the photovoltaic grid-connected power generation state. After the specific steps adopted by the grid-side relay topology self-test method are implemented, it seamlessly integrates with the normal operation of the photovoltaic energy storage inverter system, without redundant logic, making it very suitable for programming implementation in digital control.

[0096] DelayTime1, DelayTime2, DelayTime3, DelayTime4, and DelayTime5 are the times when a certain time delay is implemented. This delay takes into account the time required for all relay contact state switching and the necessary delay to ensure reliable fault detection. The fault diagnosis and detection logic of all relays in S1 and S2 of the relay combination detection method is similar. Furthermore, when all selected relay models are the same, the delay after relay state switching can be the same as described above. Therefore, these two identical relay topology self-test algorithms can be written as subroutines, thus achieving program modularity. These subroutines are then called sequentially in the self-test program, and each call only requires the effective value of the load terminal voltage v. acms Effective value of grid voltage v grms and the effective value of the inverter's AC output voltage V invrms The self-test of the grid-side relay topology can be achieved by replacing the formal parameters of the subroutine; wherein, the effective value of the load-side voltage v acms Effective value of grid voltage v grms and the effective value of the inverter's AC output voltage V invrms It is based on the sampled load terminal voltage v ac Grid voltage v g and inverter AC output voltage V inv The instantaneous voltage is calculated and implemented in the program. Since the energy storage inverter control has already sampled these voltage signals, the self-test method does not require additional hardware, which shows that the self-test method has low cost.

[0097] For the grid-side relay topology of the energy storage inverter, the logic involved in the self-testing method simultaneously considers the functional requirements of both grid-connected and off-grid operation modes, as well as the characteristic of supplying power to the backup load in both modes, thus balancing grid-connection requirements and UPS performance. Specifically, the method first performs a self-test on the relay group between the grid connection terminal and the load terminal. If the relay group is fault-free, it is in grid-connected load mode after the self-test, meaning the grid supplies power to the backup load, ensuring power to the backup load. Secondly, it performs a self-test on the relay between the inverter's AC output terminal and the AC bus in the energy storage inverter system. If the relay is fault-free, its contacts close after the self-test, indicating grid-connected operation. When photovoltaic modules are present in the system, grid-connected photovoltaic power generation can be achieved. Clearly, the grid-side relay topology self-testing method seamlessly integrates with the functions of the photovoltaic energy storage inverter system, has no redundant logic, and is suitable for programming implementation in digital control.

[0098] In this embodiment, preferably, the power grid failure fault is determined as follows:

[0099] A voltage setting value for grid power failure is set, and a grid power failure filtering window is given. If the grid voltage is lower than the voltage setting value for grid power failure, corresponding to a fixed number of low-voltage counting points, and the number of low-voltage counting points lower than the voltage setting value for grid power failure counted in the grid power failure filtering window is greater than the fixed number of low-voltage counting points, it is determined that a grid power failure has occurred at this time.

[0100] If the number of low-voltage counting points counted in the power grid failure filtering window that is lower than the set value of the power grid voltage failure is less than the fixed number of low-voltage counting points, it is determined that the power grid is normal at this time, that is, no power failure has occurred.

[0101] The method for rapid detection of mains power failure in the grid-side relay topology of the main circuit of the energy storage inverter can quickly identify the mains voltage failure when a mains power failure occurs, and send a control command to the grid-side relay topology to quickly disconnect the relays RY2 and RY3 in the grid-side relay topology. At the same time, the inverter switches from current-type control mode to voltage-type control mode to provide uninterrupted energy for the backup load.

[0102] It should be noted that the flowchart of the digital control algorithm for the grid-side relay topology detection method is as follows: Figure 3 , Figure 4 and Figure 5 As shown; Figure 3 It is the initialization part of the main program in the energy storage system, which implements the initialization of all relay coils in the grid-side relay topology when they are de-energized; Figure 4The logic for calling the S1 subroutine is given, defining the formal parameters relays RY2 and RY3, and the effective value of the mains voltage V. g_Rms and the effective value of the load voltage V ac_Rms ; Figure 5 The logic for calling the S2 subroutine is given, and the formal parameter relay RY1 and the effective value of the mains voltage V are defined. g_Rms and the effective value of inverter output voltage V inv_Rms ; Figure 4 and Figure 5 Static variables are defined: relay self-test timer / counter s_u16Cnt_RelayChecK, relay short-circuit fault counter s_u16Cnt_RelayShortChecK, relay open-circuit counter s_u16Cnt_RelayOpenChecK, and relay voltage error_VoltageError_Relay. When the relay self-test calls this subroutine, as long as the self-test is not completed, this subroutine will be continuously called by the self-test program segments of relays RY2 and RY3. Figure 4 Each time this subroutine is called, the relay self-test timer counter s_u16Cnt_RelayChecK increments by 1. Therefore, s_u16Cnt_RelayChecK reflects the number of times the subroutine is called. If the self-test program segment of the relay group is executed in the task of the TMS320F28035 controller, then the interval between each call of this subroutine should be determined by the time of entering the task. Therefore, the time delay in the relay detection process can be obtained by the number of times the subroutine is called. That is, the time delay can be accurately realized by the relay self-test timer counter s_u16Cnt_RelayChecK, thereby obtaining the times DelayTime1, DelayTime2, DelayTime3, DelayTime4, and DelayTime5, and these times can be represented by the value of s_u16Cnt_RelayChecK in the program.

[0103] When relays RY2 and RY3 perform self-test, call Figure 4 In the subroutine of the algorithm flow, during the process of counting to DelayTime3 in s_u16Cnt_RelayChecK, by Figure 4It is known that when this subroutine is called, since s_u16Cnt_RelayChecK = 0, relay RY2 is closed and relay RY3 is released (implemented using Relay2_ON and Relay3_OFF instructions); at DelayTime1, both relays RY2 and RY3 are released (implemented using Relay2_OFF and Relay3_OFF instructions); at DelayTime2, relay RY2 is released and relay RY3 is closed (implemented using Relay2_OFF and Relay3_ON instructions);

[0104] at DelayTime3, both relays RY2 and RY3 are closed (implemented using Relay2_ON and Relay3_ON instructions); that is, during the process of s_u16Cnt_RelayChecK counting to DelayTime3, at least one relay in the relay group is open. Therefore, when s_u16Cnt_RelayChecK < DelayTime3, the effective voltage values at both ends of a certain group of relays are subtracted to obtain the effective voltage value error at both ends of the relay group, that is, VoltageError_Relay = V g_Rms –V ac_Rms , and the absolute value abs(VoltageError_Relay) of VoltageError_Relay should be close to the effective value of the grid voltage and should be relatively large, indicating that relays RY2 and RY3 have not suffered a short - circuit fault. Otherwise, if it is too small, it indicates that there is a short - circuit fault in this group of relays. To implement this logic, in the program, to ensure the rigor of the logic, a relay short - circuit fault flag bit g_SysFaultMessage.bit.RelayShort is set, and g_SysFaultMessage.bit.RelayShort = 0 indicates that there is no relay short - circuit fault, while g_SysFaultMessage.bit.RelayShort = 1 indicates that a relay short - circuit fault has occurred; moreover, the program enters the short - circuit fault judgment under the premise that g_SysFaultMessage.bit.RelayShort = 0, mainly to avoid executing this section of the program subsequently if a short - circuit fault occurs, thereby improving the execution efficiency of the overall program;

[0105] Under the premise that no short-circuit fault has occurred, if the absolute value of the voltage effective value error abs(VoltageError_Relay) is less than 10V, indicating that it is close to 0, then a short-circuit fault has occurred. To achieve reliable and accurate detection results, this subroutine sets a short-circuit fault counter s_u16Cnt_RelayShortChecK. A relay short-circuit fault is only confirmed after abs(VoltageError_Relay) has been less than 10V 50 times. This serves as digital filtering to prevent misjudgments caused by interference. Once a short-circuit fault is confirmed, the subroutine then sets the relay self-test timer counter s_u16Cnt_ The RelayChecK is cleared to prevent the self-test program from executing further. At the same time, the short-circuit fault counter s_u16Cnt_RelayShortChecK is cleared to prepare for the next self-test after the fault is cleared. The relay short-circuit fault flag g_SysFaultMessage.bit.RelayShort=1 is set to notify the user to clear the fault and release the relay (de-energize the relay coil). If no short-circuit fault occurs, the short-circuit fault counter s_u16Cnt_RelayShortChecK is cleared to eliminate false counts caused by possible interference, and the open-circuit fault detection of relays RY2 and RY3 is entered.

[0106] From the above analysis, we know that when s_u16Cnt_RelayChecK counts to DelayTime3, both relays RY2 and RY3 are closed (implemented using Relay2_ON and Relay3_ON instructions). To ensure reliable closure of the contacts of the two relays, the program delays the open-circuit fault detection until DelayTime4. When both relays RY2 and RY3 are closed, the effective voltage difference between the two relays should be close to zero. Figure 4 When s_u16Cnt_RelayChecK > DelayTime4, the effective voltage values ​​across relays RY2 and RY3 are subtracted to obtain the effective voltage error across the relays, i.e., VoltageError_Relay = V. g_Rms –V ac_RmsFurthermore, if the absolute value of VoltageError_Relay, abs(VoltageError_Relay), is close to 0 and therefore small, it indicates that relays RY2 and RY3 have not experienced an open-circuit fault. Otherwise, if it is too large, it indicates that the group of relays has experienced an open-circuit fault. To ensure the logic's robustness, the program sets a relay open-circuit fault flag, g_SysFaultMessage.bit.RelayOpen. g_SysFaultMessage.bit.RelayOpen = 0 indicates no open-circuit fault, while g_SysFaultMessage.bit.RelayOpen = 1 indicates an open-circuit fault. The program enters the open-circuit fault judgment only when g_SysFaultMessage.bit.RelayOpen = 0, primarily to avoid re-executing this section of code if an open-circuit fault occurs, thus improving overall program efficiency. Under the premise that no open-circuit fault has occurred, if the error of the effective voltage value... If the absolute value abs(VoltageError_Relay) is greater than 30V, it indicates that the voltage is relatively large and close to the effective value of the mains voltage, thus indicating an open circuit fault. To achieve reliable and accurate detection results, this subroutine sets a relay open circuit fault counter s_u16Cnt_RelayOpenChecK. An open circuit fault is only confirmed after abs(VoltageError_Relay) has been less than 10V 50 times. This serves as a digital filter to prevent misjudgments caused by interference. Once an open circuit fault is confirmed, the subroutine clears the relay self-test timer counter s_u16Cnt_RelayChecK to zero, preventing the self-test program from continuing. Simultaneously, it clears the relay open circuit fault counter s_u16Cnt_RelayOpenChecK to zero, preparing for the next self-test after the fault is cleared. The relay short circuit fault flag g_SysFaultMessage.bit.RelayOpen=1 is set to notify the user to clear the fault and release the relay (de-energize the relay coil). This relay open-circuit fault self-test continues until DelayTime5. If no open-circuit fault occurs during this period, the open-circuit fault counter s_u16Cnt_RelayOpenChecK is cleared to eliminate false counts caused by possible interference, and the relay self-test pass flag g_StateChecK.bit.AcRlyChecKOver is set to 1.Clear the relay self-check timing counter s_u16Cnt_RelayChecK, relay open-circuit fault counter s_u16Cnt_RelayOpenChecK, and relay short-circuit fault counter s_u16Cnt_RelayShortChecK, so as to prepare for the self-check of relay RY1.

[0107] After the self-check of relays RY2 and RY3 is completed, call the self-check of relay RY1 as shown in the subroutine of the algorithm flow (at this time, relays RY2 and RY3 are both closed, and relay RY1 is released). During the process of s_u16Cnt_RelayChecK counting to the moment DelayTime3, Figure 5 As known, when this subroutine is called, since s_u16Cnt_RelayChecK = 0, relay RY1 is disconnected (implemented by the Relay1_OFF instruction). Therefore, when s_u16Cnt_RelayChecK < DelayTime3, the effective voltage values at both ends of the relay are subtracted to obtain the effective voltage value error at both ends of the relay, that is, VoltageError_Relay = V Figure 5 –V g_Rms –V inv_RmsFurthermore, the absolute value of VoltageError_Relay, abs(VoltageError_Relay), should be close to the effective value of the mains voltage and therefore should be relatively large. This indicates that the relay has not experienced a short circuit fault. Otherwise, if it is too small, it indicates that the relay has experienced a short circuit fault. To ensure the meticulousness of this logic, the program sets a relay short circuit fault flag, g_SysFaultMessage.bit.RelayShort. g_SysFaultMessage.bit.RelayShort=0 indicates that no relay short circuit fault has occurred, while g_SysFaultMessage.bit.RelayShort=1 indicates that a relay short circuit fault has occurred. Moreover, the program enters the short circuit fault judgment under the premise that g_SysFaultMessage.bit.RelayShort=0, mainly so that if a short circuit fault occurs, this section of the program does not need to be executed again, thereby improving the overall program execution efficiency. Under the premise that no short-circuit fault has occurred, if the absolute value of the voltage RMS error abs(VoltageError_Relay) is less than 10V, indicating that it is close to 0, then a short-circuit fault has occurred. To achieve reliable and accurate detection results, this subroutine sets a short-circuit fault counter s_u16Cnt_RelayShortChecK. A relay short-circuit fault is only confirmed after abs(VoltageError_Relay) has been less than 10V 50 times. This serves as a digital filter to prevent interference from causing a short circuit. To prevent misjudgments, once a short-circuit fault is confirmed, this subroutine clears the relay self-test timer counter s_u16Cnt_RelayChecK to prevent further execution of the self-test program. Simultaneously, it clears the short-circuit fault counter s_u16Cnt_RelayShortChecK to prepare for the next self-test after the fault is cleared. It also sets the relay short-circuit fault flag g_SysFaultMessage.bit.RelayShort=1 to notify the user to clear the fault and release the relay (de-energize the relay coil). If no short-circuit fault occurs, the short-circuit fault counter s_u16Cnt_RelayShortChecK is cleared to eliminate possible miscounts caused by interference, and the subroutine proceeds to the relay open-circuit fault detection.

[0108] From the above analysis, we know that when s_u16Cnt_RelayChecK counts to DelayTime3, relay Relay1 closes (implemented using the Relay1_ON instruction). To ensure reliable contact closure of the relays, the program delays until DelayTime4 before performing open-circuit fault detection. When all relays are closed, the effective voltage difference across the relays should be close to zero. Figure 5When s_u16Cnt_RelayChecK > DelayTime5, the effective voltage values ​​across the relay are subtracted to obtain the effective voltage error across the relay, i.e., VoltageError_Relay = Vg_Rms – Vinv_Rms. The absolute value of VoltageError_Relay, abs(VoltageError_Relay), should be close to 0 and therefore small, indicating that the relay has not experienced an open circuit fault. Otherwise, if it is too large, it indicates that the relay has experienced an open circuit fault. To ensure the meticulousness of this logic, the program sets a relay open circuit fault flag bit g_SysFaultMessage.bit.RelayOpen, where g_SysFaultMessage.bit.RelayOpen = 0 indicates that no relay open circuit fault has occurred, and g_SysFaultMessage.bit.RelayOpen = 1 indicates that an open circuit fault has occurred. Furthermore, the program enters the open-circuit fault judgment only when `g_SysFaultMessage.bit.RelayOpen=0`. This is primarily to avoid re-executing this section of the program if an open-circuit fault occurs, thus improving the overall program efficiency. If, assuming no open-circuit fault has occurred, the absolute value of the voltage RMS error `abs(VoltageError_Relay)` is greater than 30V, indicating a large error close to the mains voltage RMS value, then an open-circuit fault has occurred. To achieve reliable and accurate detection results, this subroutine sets a relay open-circuit fault counter `s_u16Cnt_RelayOpenChecK`. An open-circuit fault is only confirmed after `abs(VoltageError_Relay)` has been less than 10V 50 times; this serves as a digital filter. To prevent misjudgments caused by interference, once an open-circuit fault is confirmed, this subroutine clears the relay self-test timer counter s_u16Cnt_RelayChecK to zero, preventing the self-test program from continuing. Simultaneously, it clears the relay open-circuit fault counter s_u16Cnt_RelayOpenChecK to zero, preparing for the next self-test after the fault is cleared. It also sets the relay short-circuit fault flag g_SysFaultMessage.bit.RelayOpen=1 to notify the user to clear the fault and release the relay (de-energizing the relay coil). This relay open-circuit fault self-test continues until DelayTime5. If no open-circuit fault occurs during this time, the open-circuit fault counter s_u16Cnt_RelayOpenChecK is cleared to eliminate possible miscounts caused by interference, and the relay self-test pass flag g_StateChecK.bit.AcRlyChecKOver=1.Then, clear the relay self-test timer counter s_u16Cnt_RelayChecK, the relay open circuit fault counter s_u16Cnt_RelayOpenChecK, and the relay short circuit fault counter s_u16Cnt_RelayShortChecK.

[0109] In the self-test method of the network-side relay topology, relays RY2 and RY3 can be tested through S1. Figure 4 The subroutine call implements self-testing; relay RY1 in S2 can be used via... Figure 5 The subroutine call implements self-testing. In summary, this invention employs a detection method based on corresponding relay combinations, which facilitates modular programming, making it suitable for digital control. The program requires minimal resources and requires no additional hardware overhead.

[0110] The subroutine for the rapid detection method of mains power failure faults has been optimized. Its principle and program are as follows: Figure 6 and Figure 7 As shown. Figure 6 The grid voltage is represented by a sine curve in the figure, and the grid power outage voltage setting is represented by the two straight lines in the figure. By comparing the instantaneous value of the actual grid sampling with the grid power outage voltage setting, the red area represents a fixed low-voltage counting area corresponding to the voltage below the grid power outage voltage setting. When the number of low-voltage count points below the grid voltage power outage set value counted in the grid power outage filtering window is greater than the fixed number of low-voltage count points, it is determined that a grid power outage fault has occurred. If the number of low-voltage count points below the grid voltage power outage set value counted in the grid power outage filtering window is less than the fixed number of low-voltage count points, it is determined that the grid is normal at this time, i.e., no power outage fault has occurred. The fast detection method for mains power outage faults in the grid-side relay topology of the energy storage inverter can quickly determine the grid voltage power outage fault when a mains power outage occurs, and send a control command to the grid-side relay topology to quickly disconnect relays RY2 and RY3 in the grid-side relay topology. At the same time, the inverter (bidirectional AC / DC) is switched from current-type control mode to voltage-type control mode to provide uninterrupted energy to the backup load. Figure 7The logic of the subroutine for the rapid detection method of mains power failure described in the invention is given, defining the formal parameter GetRealValue.i32VGrid_R (actual value of grid voltage sampling), grid relays GridRelay1 (corresponding to relay RY2 in the relay topology of this invention) and GridRelay2 (corresponding to relay RY3 in the relay topology of this invention); and defining the static variables Quarter_Crossing_Flag (grid quarter-cycle flag), g_StateCheck.bit.Bypass (bypass flag), SwitchNum_OnorOffGrid (voltage setting value for grid failure), and Grid_Fault_count (number of low-voltage counters). The subroutine for the rapid detection method of mains power failure is continuously called when the grid supplies power to the backup load.

[0111] Depend on Figure 7 Knowing that after the sine wave clock completes a quarter cycle, the Quarter_Crossing_Flag flag is set to 1, and it checks if it's in bypass mode. If bypass mode is detected, the g_StateCheck.bit.Bypass flag is set to 1. At this point, within a given power outage filtering window, the actual sampled value GetRealValue.i32VGrid_R is compared with the power outage voltage setting SwitchNum_OnorOffGrid. When the sampled power grid voltage is less than the comparison voltage setting, the low-voltage count Grid_Fault_count is incremented, counting the number of power grid error points in the power outage filtering window. In the program, the power outage voltage setting SwitchNum_OnorOffGrid is set to 138, and the effective value of the abnormal power grid voltage is set to 220V. The angle is calculated in reverse. Since the interrupt period configured in the program is 100μs and a quarter-cycle of the power grid is 5ms, it is calculated that there are 50 counting points in one quarter-cycle. Therefore, the fixed number of low-voltage counting points allowed in one power grid cycle can be determined. The number of points is set to 16 in the margin program. When the number of low-voltage counting points counted within a quarter of the grid cycle is greater than 16, the grid-side relays GridRelay1 (corresponding to relay RY2 in the relay topology of this invention) and GridRelay2 (corresponding to relay RY3 in the relay topology of this invention) are disconnected, and the inverter changes from current-type to voltage-type, thereby realizing safe off-grid operation under abnormal grid conditions.

[0112] Figure 8 The program description for switching between grid connection and off-grid is provided. The left side shows the program logic for switching from grid connection to off-grid, and the right side shows the program logic for switching from off-grid to grid connection.

[0113] Grid-connected and off-grid switching

[0114] When a grid fault is detected (according to the above-mentioned rapid detection method for mains power failure faults, when the number of low-voltage counters Grid_Fault_count is greater than 16, it is determined that a grid failure fault has occurred at this time), the following steps will be executed: PWMOutputsDisable() will be disabled, and the inverter output relay OffGridRelay (corresponding to relay RY1 in the relay topology of this invention) and grid-side relays GridRelay1 (corresponding to relay RY2 and GridRelay2 in the relay topology of this invention) and GridRelay2 (corresponding to relay RY3 in the relay topology of this invention) will be disconnected. After determining that the on-grid / off-grid flag OnOffGridFlag is in an off-grid state, the inverter output becomes voltage-type off-grid. Inverter_Operating() will be delayed for 0.8ms, and then PWMOutputsEnable() will be enabled, turning on the inverter output relay OffGridRelay.

[0115] Offline to Inline Switching

[0116] When the grid is detected to have returned to normal for 15 seconds (the program's condition is that the number of grid fault recovery points s_u16Cnt_GridVoltR_Fault_Back is greater than 750), and phase-locking is successful (the program's condition is that the phase-locking success flag phaseIntoLocked is 1), after the above two conditions are met, the blocking driver PWMOutputsDisable() is executed and the inverter output relay OffGridRelay (corresponding to relay RY1 in the relay topology of this invention) and grid-side relays GridRelay1 (corresponding to relay RY2 and GridRelay2 in the relay topology of this invention) and GridRelay2 (corresponding to relay RY3 in the relay topology of this invention) are disconnected. After determining that the grid connection / off-grid flag OnOffGridFlag is in grid connection status, the bypass program is executed to change the voltage-type off-grid inverter to a current-type grid-connected inverter. After a delay of 0.8ms in Bypass_Processing(), the grid-side relays GridRelay1 and GridRelay2 are turned on, and the system state g_Sys_Current_State is set to the waiting state WaitState.

[0117] Energy control strategy of grid-side relay topology in energy storage inverter: During operation of the main circuit of energy storage inverter, when there is no grid fault, but a grid fault occurs:

[0118] When a grid fault occurs, relays RY2 and RY3 are disconnected, and the inverter switches from current-mode control to voltage-mode control to provide uninterrupted energy to the backup load.

[0119] When the power grid returns to normal, the inverter, after achieving phase amplitude tracking of the power grid, disconnects relay RY1 and simultaneously closes relays RY2 and RY3, so that the power grid prioritizes power supply to the backup load.

[0120] Embodiments of the present invention:

[0121] like Figure 9 In the application example of the circuit shown, the main parameters are configured as follows: Relays RY1, RY2, and RY3 are all Tycor T92P7D12-12 relays with a coil voltage of 12V and two sets of normally open contacts. The maximum power of the energy storage inverter is 5KW, the DC bus (high voltage DC side) voltage Vbus=400V, the energy storage battery voltage is 48V-63V, the MPPT voltage range of the PV module is 200V-440V, the AC side output AC current is 23A, and the grid rated voltage is 230V / 50Hz. The grid-side relay control signals Vr1, Vr2, and Vr3 are generated by the general-purpose I / O ports GPIO22, GPIO41, and GPIO44 of the TI DSP model TMS320F28035, and then powered by the corresponding driver circuits 1, 2, and 3 to supply power to the coils of relays RY1, RY2, and RY3. In the TMS320F28035 controller, GPIO22, GPIO41, and GPIO44 are configured as output I / O ports and initialized to low level. When the corresponding GPIO port outputs Vr1, Vr2, and Vr3 are high level, the coils of the corresponding relays RY1, RY2, and RY3 are energized, thereby controlling the normally open contacts of relays RY1, RY2, and RY3 to close. Conversely, when Vr1, Vr2, and Vr3 are low level, the normally open contacts of relays RY1, RY2, and RY3 are opened, and the relays are released. After the energy storage inverter is powered on, the initialization program in the DSP controller sets the control signals Vr1, Vr2, and Vr3 of all relays in the grid-side relay topology to low level, thereby controlling the coils of relays RY1, RY2, and RY3 to de-energize, causing their normally open contacts to be in the released state.

[0122] Figure 9 In this example, the backup load is connected to the AC bus side. Power can be supplied from the grid by controlling grid-side relays RY2 and RY3. When a grid power failure occurs, energy can be supplied to the backup load by the inverter in the energy storage inverter through relay state switching, ensuring uninterrupted power supply. Figure 4 Subroutine calls can achieve Figure 9 The self-test of the RY2 and RY3 relay topologies uses... Figure 5 Subroutine calls can achieve Figure 9In the self-test example program for the RY1 relay topology, the times corresponding to DelayTime1, DelayTime2, DelayTime3, DelayTime4, and DelayTime5 are obtained by counting delays from the relay self-test timer / counter s_u16Cnt_RelayChecK, and are set to 1 second, 1.2 seconds, 2.2 seconds, 2.4 seconds, and 3.4 seconds respectively. Since the relay self-test program segment in the example is executed within a state machine task, and the state machine task time is configured to 2ms by the program, DelayTime1, DelayTime2, DelayTime3, DelayTime4, and DelayTime5 are... Figure 4 The values ​​are set to 500, 600, 1100, 1200, and 1700.

[0123] use Figure 7 The subroutine for the rapid detection method of mains power failure can be called to quickly determine the mains power failure. The program configures the mains power failure voltage setting value SwitchNum_OnorOffGrid=138. The low voltage count point Grid_Fault_countMax calculated according to the voltage of the mains power failure voltage setting value is 14. To consider the safety margin and prevent false triggering, the low voltage count point Grid_Fault_countMax is set to 16.

[0124] use Figure 8 Subroutine calls enable the photovoltaic inverter to automatically switch to off-grid operation during grid faults and prepare for reconnection when the grid is restored, providing safe switching control logic. In the application example of the circuit of this invention, OffGridRelay corresponds to relay RY1 in the grid-side relay topology of the energy storage inverter; GridRelay1 corresponds to relay RY2 in the grid-side relay topology of the energy storage inverter; and GridRelay2 corresponds to relay RY3 in the grid-side relay topology of the energy storage inverter.

[0125] Based on the above analysis, the energy storage inverter can only enter normal operation after the grid-side relay topology has no faults during self-testing. Figure 10 Application examples of the present invention are given. Figure 9 The experimental waveform of the system switching from grid-connected to off-grid when it detects a power outage fault is shown. Figure 10 Channel CH1 in the diagram represents the backup load voltage V. ac Waveform, channel CH3 is the grid current i g Waveform, channel CH4 is the grid voltage v gThe waveform shows a measured switching time of Δx = 4.8ms, which is much smaller than the 20ms requirement specified in the relevant standards for energy storage inverters, thus meeting the energy control performance requirements for uninterrupted power supply to backup loads.

[0126] As described above, the self-testing method and energy control strategy of the grid-side relay topology in the energy storage inverter of the present invention can be composed of three relays with two sets of normally open contacts. If the grid-side relay topology of the present invention uses a relay with only one set of normally open contacts, then six relays are required. In this case, the coils of the two corresponding relays in the L line and N line should use the same control signal.

[0127] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A grid-side relay topology system for an energy storage inverter, characterized in that, It includes an energy storage inverter main circuit and a control system. The energy storage inverter main circuit includes a grid-side relay topology, and the control system is electrically connected to the energy storage inverter main circuit. The network-side relay topology consists of relays RY1, RY2, and RY3. Relays RY1, RY2, and RY3 are divided into two combinations. The first combination module is composed of relays RY2 and RY3, and the second combination module is composed of relays RY1. The normally open contacts of relays RY2 and RY3 in the first combination module are connected in series to form a first bridge arm. One end of the first bridge arm is connected to the grid terminal, and the other end of the first bridge arm is connected to the AC bus. A backup load is electrically connected to the AC bus. The relay RY1 in the second combination module forms a second bridge arm. One end of the second bridge arm is connected to the AC output terminal of the inverter, and the other end of the second bridge arm is connected to the AC bus.

2. The grid-side relay topology system in the energy storage inverter according to claim 1, characterized in that, The other end of the inverter is connected to a high-voltage side DC bus. The other side of the high-voltage side DC bus is electrically connected to an MPPT controller and a battery charging and discharging circuit. A photovoltaic module is electrically connected to the MPPT controller, and an energy storage battery is electrically connected to the battery charging and discharging circuit.

3. The grid-side relay topology system of the energy storage inverter according to claim 2, characterized in that, The control system includes a signal acquisition and fault detection system, a drive controller, and a TMS320F28035 controller. The signal acquisition and fault detection system is used to acquire voltage signals from the grid terminals and the energy storage battery, and to perform fault analysis and processing. The TMS320F28035 controller is electrically connected to the signal acquisition and fault detection system via AD sampling, and is used to perform AD signal sampling on the signal acquisition and fault detection system.

4. The grid-side relay topology system of the energy storage inverter according to claim 3, characterized in that, The TMS320F28035 controller is configured with GPIO22, GPIO41, and GPIO44 as output I / O ports. The TMS320F28035 controller transmits the acquired AD signal to the coil and driver of relay RY1, the coil and driver of relay RY2, and the coil and driver of relay RY3 through the output I / O ports of GPIO22, GPIO41, and GPIO44. The driver is used to power the coils of relays RY1, RY2, and RY3, thereby controlling the closing of the normally open contacts of relays RY1, RY2, and RY3.

5. A self-testing method for the grid-side relay topology in an energy storage inverter, characterized in that, The method is used to perform the self-testing method of the grid-side relay topology by means of the first combination module and the second combination module in claims 1-4. When the mains power fails, the combined detection of the first combination module and the second combination module is used. When the grid is normal, the grid-side relay topology needs to be self-tested before the main circuit of the energy storage inverter is running normally. At this time, the inverter in the main circuit of the energy storage inverter does not work. Includes the following steps: S1. The combination of relays RY2 and RY3 is used to detect whether a short circuit fault or an open circuit fault has occurred at their contacts; S2. Relay RY1 is used to detect whether a short circuit or open circuit fault has occurred at its contacts.

6. The self-testing method for the grid-side relay topology in an energy storage inverter according to claim 5, characterized in that, The specific operation procedure for detecting whether the contacts of relays RY2 and RY3 in S1 have short circuit or open circuit faults is as follows: During the initialization phase, the coils of relays RY2 and RY3 are de-energized, and the contacts are in the released state. Subsequently, the response characteristics of contact closing and releasing are verified by alternately driving relay RY2 to be energized, relay RY3 to be de-energized, and both coils to be energized and de-energized simultaneously. During the delay period from DelayTime1 to DelayTime4, the difference between the effective value of the grid voltage and the effective value of the backup load voltage is continuously monitored. If the difference approaches 0, it is determined to be a short circuit fault. If the difference is stable and close to the grid voltage, it is determined to be an open circuit fault.

7. The self-testing method for the grid-side relay topology in an energy storage inverter according to claim 6, characterized in that, The specific steps by which the relay RY1 in S2 detects whether its contacts have short-circuit or open-circuit faults are as follows: With relay RY2 or relay RY3 closed, the coil of relay RY1 is first de-energized to release its contacts. Then, during the DelayTime3 phase, the coil of relay RY1 is energized, causing the normally open contacts of both relay RY1 and relay RY2 to close. During the DelayTime4 phase, the effective value difference between the grid voltage and the inverter output voltage is continuously monitored. If the difference is close to 0, a short circuit fault is determined for relay RY1; otherwise, an open circuit fault detection is initiated. If the difference continues to be close to the effective value of the grid voltage, an open circuit fault is determined.

8. The self-testing method for the grid-side relay topology in an energy storage inverter according to claim 7, characterized in that, The power grid failure fault setting criteria are as follows: A voltage setting value for grid power failure is set, and a grid power failure filtering window is given. If the grid voltage is lower than the voltage setting value for grid power failure, corresponding to a fixed number of low-voltage counting points, and the number of low-voltage counting points lower than the voltage setting value for grid power failure counted in the grid power failure filtering window is greater than the fixed number of low-voltage counting points, it is determined that a grid power failure has occurred at this time. If the number of low-voltage counting points counted in the power grid failure filtering window that is lower than the set value of the power grid voltage failure is less than the fixed number of low-voltage counting points, it is determined that the power grid is normal at this time, that is, no power failure has occurred. The method for rapid detection of mains power failure in the grid-side relay topology of the main circuit of the energy storage inverter can quickly identify the mains voltage failure when a mains power failure occurs, and send a control command to the grid-side relay topology to quickly disconnect relays RY2 and RY3 in the grid-side relay topology. At the same time, it allows the inverter to switch from current-type control mode to voltage-type control mode to provide uninterrupted energy for the backup load.

9. An energy control strategy for a grid-side relay topology in an energy storage inverter, the strategy being used to provide uninterrupted energy to the backup load as described in claims 4-8; characterized in that, The mains power supply to the energy storage inverter is fault-free during operation, but a grid fault occurs: When a grid fault occurs, relays RY2 and RY3 are disconnected, and the inverter switches from current-mode control to voltage-mode control to provide uninterrupted energy to the backup load. When the power grid returns to normal, the inverter, after achieving phase amplitude tracking of the power grid, disconnects relay RY1 and simultaneously closes relays RY2 and RY3, so that the power grid prioritizes power supply to the backup load.

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