A kind of on-grid and off-grid parallel system and control method thereof

Abstract

The present invention relates to the field of energy storage and off-grid control technology, and in particular to an on-grid and off-grid parallel system and its control method. The number of the electric cabinets is N, and each of the electric cabinets is provided with a plurality of battery modules, the plurality of battery modules are connected to the control box through insulated cables, and the control box is pre-charged and connected to the PCS energy storage inverter module; the PCS energy storage inverter module is connected to the backup power supply end of one STS module, and the main power supply end of the other STS module is connected to the municipal power grid, and the output end of the municipal power grid in the STS module and the output end of the PCS energy storage inverter module are connected to the load end, so that the on-grid and off-grid can be seamlessly switched. The present invention can realize on-grid and off-grid switching power supply, so that it can continuously supply power to important power loads, so that the key loads can operate uninterruptedly and stably, avoid the losses caused by power outages, and improve the flexibility, safety and operation stability of the system power supply.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage grid-connected and off-grid control, and in particular to a grid-connected and off-grid parallel system and a control method thereof. Background Art

[0002] The on-grid and off-grid parallel system is an electric energy management system, which includes the on-grid (connected to the public power grid) and off-grid (detached from the public power grid) operation modes of power equipment, so that the system can be switched under different circumstances to ensure the stability and flexibility of the load power supply. However, the existing on-grid and off-grid parallel systems usually require the use of multiple switching switches for on-grid and off-grid switching, which greatly reduces the on-grid and off-grid efficiency of the load-side power supply, and the control of multiple switching switches is prone to on-grid and off-grid mode switching control errors, resulting in delays, inability to switch, and short circuits during on-grid and off-grid switching, increasing the probability of power supply safety accidents, reducing the safety factor, and poor reliability; and the switching time of multiple switching switches is long, which is difficult to meet the actual power usage needs. Therefore, it is necessary to develop a stable and efficient on-grid and off-grid parallel system to solve the above problems. Summary of the invention

[0003] The present invention overcomes the shortcomings of the prior art and provides an on-grid and off-grid parallel system and a control method thereof.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] The present invention provides an on-grid and off-grid parallel system, the on-grid and off-grid parallel system comprising a backup power supply end, the backup power supply end being provided with an electric cabinet:

[0006] The number of the electric cabinets is N, and each of the electric cabinets is provided with a plurality of battery modules, the plurality of battery modules are connected to a control box through insulating cables, and the control box is pre-charged and grid-connected to a PCS energy storage converter module;

[0007] The PCS energy storage converter module is connected to the backup power supply end of one STS module, and the main power supply end of another STS module is connected to the municipal power grid, and the output end of the municipal power grid in the STS module and the output end of the PCS energy storage converter module are connected to the load end, so that the grid connection and off-grid connection can be seamlessly switched;

[0008] The grid-end input interface of each of the electric cabinets is connected to the grid combiner cabinet after passing through the STS module. An EPS load combiner cabinet is arranged next to the grid combiner cabinet. The EPS load combiner cabinet is connected to the load-end output interface of each of the electric cabinets through an insulated cable.

[0009] The distances between the N electric cabinets and the grid combiner cabinet and the EPS load combiner cabinet are not uniform, and the length difference of the insulated cables connecting the grid end and the load end of each electric cabinet to the grid combiner cabinet and the EPS load combiner cabinet does not exceed 5%.

[0010] Furthermore, in a preferred embodiment of the present invention, the PCS energy storage converter module includes a soft start circuit, a grid-connected relay is provided in the soft start circuit, and the soft start circuit is connected to the STS module via the grid-connected relay.

[0011] Furthermore, in a preferred embodiment of the present invention, the grid-connected relay is connected to a loop outlet of the AC filter loop, and a loop inlet of the AC filter loop is connected to a bidirectional inverter unit.

[0012] Furthermore, in a preferred embodiment of the present invention, the bidirectional inverter unit is arranged in a soft-start circuit, and the soft-start circuit is connected to an AC lightning protection module via an insulated cable.

[0013] Furthermore, in a preferred embodiment of the present invention, the STS module includes an STS static switching switch, a plurality of first bidirectional thyristors are arranged inside the STS static switching switch, and the plurality of first bidirectional thyristors are connected to the PCS energy storage converter module.

[0014] Furthermore, in a preferred embodiment of the present invention, a plurality of second bidirectional thyristors are disposed inside the STS static switching switch, and the plurality of second bidirectional thyristors are connected to the grid-connected end of the municipal power grid.

[0015] A second aspect of the present invention provides a control method for an on-grid and off-grid parallel system, which is applied to any one of the on-grid and off-grid parallel systems described above, and specifically comprises the following steps:

[0016] Obtaining the actual voltage peak value and the normal voltage peak value output by the municipal power grid when the municipal power grid is in stable power supply at a predetermined monitoring time step, drawing a kurtosis diagram based on the actual voltage peak value and the normal voltage peak value, and detecting and analyzing whether the municipal power grid has a fault through the kurtosis curve of the kurtosis diagram, and if so, controlling the STS module to generate a first opening and closing instruction;

[0017] Based on the first opening and closing instruction, the second bidirectional thyristor at the grid-connected end of the municipal power grid is controlled to be disconnected and the first bidirectional thyristor of the PCS energy storage converter module is controlled to be closed, so that the grid-connected operation is switched to the off-grid operation;

[0018] If the municipal power grid is in a fault state, the real-time voltage peak value of the municipal power grid in the fault state is updated to generate a first peak model diagram, and the non-overlapping peak model area between the first peak model diagram and the second peak model diagram under the normal voltage peak value is calculated and analyzed to see whether it is less than the peak recovery area threshold value. If it is, the STS module is controlled to generate a second opening and closing instruction;

[0019] According to the second opening and closing instruction, the first bidirectional thyristor of the PCS energy storage converter module is controlled to be disconnected and the second bidirectional thyristor of the municipal power grid connected end is controlled to be closed, so that the off-grid operation is switched to the grid-connected operation;

[0020] Obtaining actual power demand of the load end, and obtaining a currently required load end operation mode according to the actual power demand;

[0021] If the load-end operation mode shows that the number of load ends actually required to be operated is N, a group of differential equations is constructed based on the historical sending timestamps when the STS module in each electrical cabinet sends the first opening and closing instructions and the second opening and closing instructions, and the STS modules of the N load ends are coordinated and synchronously controlled by solving the group of differential equations.

[0022] Furthermore, in a preferred embodiment of the present invention, the actual voltage peak value and the normal voltage peak value output by the municipal power grid when the municipal power grid is in a stable power supply at a predetermined monitoring time step are obtained, a kurtosis diagram is drawn based on the actual voltage peak value and the normal voltage peak value, and a kurtosis curve of the kurtosis diagram is used to detect and analyze whether the municipal power grid has a fault. If so, the STS module is controlled to generate a first opening and closing instruction, which specifically includes the following steps:

[0023] Acquire a monitoring strategy of the on-grid and off-grid parallel system for the municipal power grid, and extract a predetermined monitoring time step of the on-grid and off-grid parallel system for the municipal power grid through the monitoring strategy;

[0024] Obtain the normal voltage peak value output by the municipal power grid when the municipal power grid is in a stable power supply at a predetermined monitoring time step through the municipal power grid maintenance log, import multiple normal voltage peak values ​​into the kurtosis diagram for fitting and drawing, and obtain a normal voltage peak kurtosis diagram;

[0025] Obtain several real-time voltage peaks output by the current municipal power grid at a given monitoring time step, construct a kurtosis diagram, import several real-time voltage peaks output at a given monitoring time step into the kurtosis diagram for calculation and fitting, and obtain a real-time voltage peak kurtosis diagram;

[0026] Extracting a kurtosis curve of a normal voltage peak based on the normal voltage peak kurtosis diagram, extracting a kurtosis curve of a real-time voltage peak based on the real-time voltage peak kurtosis diagram, calculating a kurtosis deviation between the kurtosis curve of the normal voltage peak and the kurtosis curve of the real-time voltage peak, and obtaining a kurtosis deviation value;

[0027] An abnormal voltage kurtosis threshold is preset. If the kurtosis deviation value is greater than the abnormal voltage kurtosis threshold, the municipal power grid is calibrated as a fault state, and the STS module is controlled to generate a first opening and closing instruction.

[0028] Furthermore, in a preferred embodiment of the present invention, if the municipal power grid is in a fault state, the real-time voltage peak value of the municipal power grid in the fault state is updated to generate a first peak model diagram, and the non-overlapping peak model area between the first peak model diagram and the second peak model diagram under the normal voltage peak value is calculated and analyzed to see whether it is less than the peak recovery area threshold value. If it is less than, the STS module is controlled to generate a second opening and closing instruction, which specifically includes the following steps:

[0029] Under the fault state, the kurtosis curve of the real-time voltage peak of the municipal power grid under the fault state is updated, and a kurtosis model diagram of the real-time voltage peak under the fault state is generated, which is defined as the first peak model diagram;

[0030] Extracting a spike model diagram of a normal voltage peak value in a fault state through a normal voltage peak kurtosis diagram, defining the diagram as a second spike model diagram, and aligning and extracting a non-overlapping spike model region between the first spike model diagram and the second spike model diagram;

[0031] A peak recovery area threshold is preset. If the area value of the non-overlapping peak model area is less than the peak recovery area threshold, the municipal power grid is calibrated as a fault recovery state, and the STS module is controlled to generate a second opening and closing instruction based on the area value.

[0032] Furthermore, in a preferred embodiment of the present invention, if the load end operation mode shows that the number of load ends actually required to be operated is N, a differential equation group is constructed according to the historical sending timestamps when the STS module in each electrical cabinet sends the first opening and closing instructions and the second opening and closing instructions, and the STS modules of the N load ends are coordinated and synchronously controlled by solving the differential equation group, which specifically includes the following steps:

[0033] If the load end operation mode shows that the number of load ends actually required to be operated is N, then obtain the historical sending timestamps when the STS module in each electric cabinet sends the first opening and closing instructions and the second opening and closing instructions at the same timing;

[0034] Taking the STS module of each electric cabinet as a control point, the historical sending timestamp of each electric cabinet is interpolated and fitted at the corresponding control point by using the Lagrangian interpolation method to generate a Lagrangian curve;

[0035] Introducing the finite difference method to discretize the Lagrangian curve into a Lagrangian polynomial corresponding to each control point and constructing a differential equation, substituting each Lagrangian polynomial into the differential equation for calculation to obtain a differential equation group;

[0036] Preset the range of equation solutions that allow instantaneous time difference, solve the differential equation group, obtain the instantaneous time difference equation solution of the STS module in each electric cabinet sending the first opening and closing instruction and the second opening and closing instruction, and judge one by one whether the instantaneous time difference equation solution of each electric cabinet is within the range of equation solutions that allow instantaneous time difference;

[0037] If it is, the STS module of the power cabinet is marked as a synchronous transmission STS module, and there is no need to start the synchronous controller for coordinated control;

[0038] If not, the STS module of the power cabinet is marked as an asynchronous sending STS module, and the synchronous controller is started to perform coordinated synchronous control.

[0039] The beneficial technical effects of the present invention are:

[0040] The present invention can simulate a power outage caused by a fault in the power grid. If the voltage peak change value is greater than 10% of the normal voltage peak value, it is judged that the power grid is faulty, and the STS module sends a first opening and closing instruction to control the first bidirectional thyristor to close and the second bidirectional thyristor to open, so that the grid-connected operation of the load end is switched to off-grid operation. At this time, the grid-connected output of the load end is switched to the off-grid output, and all the power comes from the discharge of the battery module of the electric cabinet; the grid-connected switching and off-grid switching time is less than 10ms, ensuring that the load end is not disconnected during this process; when the power grid is in a fault power outage state, after voltage detection, if its voltage peak reaches 95% of the normal voltage peak value, it is judged that the power grid has restored power supply, and at the same time, the STS module sends a second opening and closing instruction to control the first bidirectional thyristor to open and the second bidirectional thyristor to close, so that the off-grid operation of the load end is switched to the grid-connected operation; at this time, the off-grid output of the electric cabinet at the load end is switched to the grid-connected output of the municipal power grid, and all the power comes from the power supply of the municipal power grid, and the off-grid switching and grid-connected time is less than 10ms. The present invention can realize on-grid and off-grid switching power supply, so that important power loads can be continuously powered, so that key loads can operate uninterruptedly and stably, avoid losses caused by power outages, and improve the flexibility, safety and operational stability of the system power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, drawings of other embodiments can be obtained based on these drawings without paying creative work.

[0042] Figure 1 This is a schematic diagram of the system structure of this on-grid and off-grid parallel system;

[0043] Figure 2 This is a structural diagram of the PCS energy storage converter module in this on-grid and off-grid parallel system;

[0044] Figure 3 This is a schematic diagram of the structure of the STS module in this on-grid and off-grid parallel system.

[0045] The following are the descriptions of the reference numerals:

[0046] 101. Electric cabinet; 102. Battery module; 103. Control box; 104. PCS energy storage converter module; 105. Soft start circuit; 106. Grid-connected relay; 107. STS module; 108. AC filter circuit; 109. Bidirectional inverter unit; 201. AC lightning protection module; 202. Main power supply end; 203. Load end; 204. STS static switching switch; 205. First bidirectional thyristor; 206. Second bidirectional thyristor; 207. Grid combiner; 208. EPS load combiner. DETAILED DESCRIPTION

[0047] In order to more clearly understand the above-mentioned purposes, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. These drawings are all simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the structures related to the present invention. It should be noted that the embodiments in this application and the features in the embodiments can be combined with each other without conflict.

[0048] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, "multiple" means two or more.

[0049] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0050] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0051] A first aspect of the present invention provides a grid-connected and off-grid parallel system, such as Figure 1-3 As shown, the on-grid and off-grid parallel system includes a backup power supply end, and an electric cabinet 101 is installed at the backup power supply end.

[0052] The number of the electric cabinets 101 is N, and each of the electric cabinets 101 is provided with a plurality of battery modules 102, the plurality of battery modules 102 are connected to a control box 103 via insulated cables, and the control box 103 is pre-charged and grid-connected to a PCS energy storage converter module 104.

[0053] The PCS energy storage converter module 104 includes a soft start circuit 105 , in which a grid-connected relay 106 is provided. The soft start circuit 105 is connected to the STS module 107 via the grid-connected relay 106 .

[0054] The grid-connected relay 106 is connected to the circuit outlet of the AC filter circuit 108 , and the circuit inlet of the AC filter circuit 108 is connected to the bidirectional inverter unit 109 .

[0055] The bidirectional inverter unit 109 is disposed in the soft-start loop 105 , and the soft-start loop 105 is connected to the AC lightning protection module 201 via an insulated cable.

[0056] It should be noted that the backup power supply end is mainly used to provide backup power for the load end. When the load end 203 is connected to the municipal power grid, the backup power supply end is in an idle state and does not need to provide backup power output. Therefore, the AC power is input into the grid end of the switch cabinet 101 through the municipal power grid. At this time, the grid-connected relay 106 is closed and the soft-start circuit 105 is turned on at the same time. By controlling the bidirectional inverter unit 109, a DC constant power channel is established to convert the AC power into constant power DC power to continuously charge the battery module 102, thereby realizing the automatic power charging reserve effect of the switch cabinet 101 when the backup power supply end is in an idle state; when a failure of the municipal power grid causes the load end 203 to need a backup power supply, the grid-connected relay 106 is also closed and the soft-start circuit 105 is turned on at the same time, and the bidirectional inverter unit 109 is controlled to make the battery module 102 in the switch cabinet 101 output a DC constant power to discharge the load or the grid on the AC side, thereby realizing the automatic discharge effect of the switch cabinet 101 when the backup power supply end is started. The present invention can realize bidirectional charging and discharging of the electric cabinet 101 through the PCS energy storage inverter module 104, and can reserve and supply backup power in the on-grid and off-grid switching state, which is a crucial prerequisite for the stable operation of the on-grid and off-grid parallel system, and further ensures the continuous, accurate and efficient operation of important loads with high reliability.

[0057] It should be noted that the AC filter circuit 108 is used to filter out redundant AC signals or noise in the soft start circuit 105 of the PCS energy storage inverter module 104, thereby improving the quality of AC power transmission and avoiding electrical signal noise interference, improving the stability and safety of the PCS energy storage inverter module 104 in bidirectional charging and discharging of the electric cabinet 101, preventing the occurrence of charging and discharging safety accidents in the on-grid and off-grid parallel system in the on-grid and off-grid switching state, and reducing the risk factor. Among them, the AC lightning protection module 201 is used to protect the soft start circuit 105 in the PCS energy storage inverter module 104 from being damaged by overvoltage shocks, which can effectively prevent the occurrence of the phenomenon of the PCS energy storage inverter module 104 caused by a large input of AC power, ensuring the safety factor of the on-grid and off-grid switching of the on-grid and off-grid parallel system, and at the same time improving the service life of the PCS energy storage inverter module 104, reducing the replacement frequency and cost.

[0058] The PCS energy storage inverter module 104 is connected to the backup power supply end of the STS module 107, and the main power supply end 202 of the other end of the STS module 107 is connected to the municipal power grid, and the output end of the municipal power grid in the STS module 107 and the output end of the PCS energy storage inverter module 104 are connected to the load end 203, so that the grid connection and off-grid connection can be seamlessly switched.

[0059] The STS module 107 includes an STS static switching switch 204 , and a plurality of first bidirectional thyristors 205 are disposed inside the STS static switching switch 204 . The plurality of first bidirectional thyristors 205 are connected to the PCS energy storage converter module 104 .

[0060] The STS static switching switch 204 is internally provided with a plurality of second bidirectional thyristors 206 , and the plurality of second bidirectional thyristors 206 are connected to the grid-connected end of the municipal power grid.

[0061] It should be noted that the STS module 107 is mainly used in conjunction with the PCS energy storage converter module 104 to play a seamless switching function between the grid and the off-grid in the system; when the municipal power grid loses power, the STS static switching switch 204 generates and issues a disconnection instruction, and controls the second bidirectional thyristor 206 to disconnect according to the disconnection instruction, and controls the first bidirectional thyristor 205 to close and connect, so that the load end is connected to the PCS energy storage converter module 104. At this time, the battery module 102 in the electrical cabinet 101 transmits power to the load end through the PCS energy storage converter module 104, so that the power consumption of the load end 203 is all derived from the discharge supply of the battery module 102 in the electrical cabinet 101, thereby realizing the PCS energy storage converter module 104 and STS. The TS static switching switch 204 cooperates to switch to the off-grid state to continue to supply power to important loads, avoiding the loss caused by the shutdown of important loads due to power outages; when the municipal power grid is restored, the STS static switching switch 204 generates and issues a closing instruction, controls the second bidirectional thyristor 206 to close the connection according to the closing instruction, and controls the first bidirectional thyristor 205 to disconnect, and the load end 203 is reconnected to the municipal power grid at the main power supply end. At this time, the power of the municipal power grid is input to the load end through the STS module 107, so that the power of the load end 203 is all derived from the main power supply end input of the municipal power grid, thereby realizing the PCS energy storage converter module 104 and the STS static switching switch 204 to switch to the grid-connected state to perform municipal power grid power supply. The present invention can realize online seamless grid-connected to off-grid and automatic off-grid to grid-connected functions through the coordinated switching effect of the STS module 107 and the PCS energy storage converter module 104, so as to achieve the effect of uninterrupted, continuous and stable power supply to key loads, improve the phenomenon that the overall operation of key loads is paralyzed due to municipal power grid failures, and meet different power requirements.

[0062] The grid-end input interface of each of the electric cabinets 101 is connected to the grid combiner cabinet 207 through the STS module 107. An EPS load combiner cabinet 208 is arranged next to the grid combiner cabinet 207. The EPS load combiner cabinet 208 is connected to the load-end output interface of each of the electric cabinets 101 through an insulated cable.

[0063] The distances between the N electric cabinets 101 and the grid combiner cabinet 207 and the EPS load combiner cabinet 208 are not uniform, and the length difference of the insulated cables connecting the grid end and the load end of each electric cabinet 101 to the grid combiner cabinet 207 and the EPS load combiner cabinet 208 does not exceed 5%.

[0064] It should be noted that it has been verified that the difference in the length of the insulating cables from the grid end and the load end of each electrical cabinet 101 to the grid junction cabinet 207EPS load junction cabinet 208 cannot exceed 5%. If the difference in the length of the insulating cables exceeds 5%, it may cause uneven current in the AC or DC input and output of the electrical cabinet, affecting the stable power supply performance of the on-grid and off-grid parallel system. At the same time, it may cause the probability of power transmission safety hazards and accidents, and increase the danger level of on-grid switching. Therefore, the difference in the length of the insulating cables does not exceed 5% to achieve a stable current sharing function between N electrical cabinets 101, thereby ensuring the safety and operational stability of the on-grid and off-grid parallel system.

[0065] In summary, when the municipal power grid is in normal operation, the default initial state of the PCS energy storage converter module 104 and the STS module 107 is grid-connected operation, and they work in the grid-connected mode. At this time, the first bidirectional thyristor 205 connected to the PCS energy storage converter module 104 is in an open state, and the second bidirectional thyristor 206 connected to the municipal power grid is in a closed state. The power of the load end 203 is all derived from the input of the grid end; when a fault occurs in the municipal power grid and causes a power outage, the STS static switching switch 204 generates and issues a disconnection command to control the second bidirectional thyristor 206 connected to the main power supply end of the municipal power grid to disconnect. The connection is opened, and the first bidirectional thyristor 205 connected to the PCS energy storage converter module 104 is closed at the same time. The power supply of the load end 203 is switched to the off-grid output. At this time, all the required power comes from the battery discharge. When the feedback signal corresponding to the first bidirectional thyristor 205 is detected, the PCS energy storage converter module 104 outputs the target voltage to restore the off-grid operating voltage to the rated value at a certain speed, and ensures that it is consistent with the initial phase of the power grid, and performs off-grid control at the rated frequency. The time for switching from the grid to the off-grid is less than 10ms, ensuring that the load end is not disconnected during this process. The switching process from the grid to the off-grid is completed. When the municipal power grid is in a faulty power outage, the default initial state of the PCS energy storage inverter module 104 and the STS module 107 is off-grid operation, and they work in off-grid mode. At this time, the first bidirectional thyristor 205 is in a closed state, and the second bidirectional thyristor 206 is in an open state. The power supply of the load end 203 is all supplied by the battery module 102 in the electrical cabinet 101; when the municipal power grid is restored to use after maintenance, the STS static switching switch 204 generates and issues a closing instruction to control the closing of the second bidirectional thyristor 206, and disconnects the first bidirectional thyristor 205 connected to the PCS energy storage inverter module 104. At this time, the power supply of the load end 203 is switched back to the grid-connected output, and all the required power comes from the power supply of the municipal power grid. The time for switching from off-grid to grid-connected is less than 10ms.

[0066] It should be noted that the switching between the grid and off-grid of N power cabinets 101 requires high synchronization, so it is necessary to ensure that the communication control instructions between the PCS energy storage converter module 104 and the STS module 107 have strong coordinated control. Therefore, in order to ensure synchronization, the present invention can effectively solve the communication control efficiency problem within the system by setting a synchronous controller, which greatly improves the switching balance and stability of the grid-connected and off-grid parallel system. When a municipal power grid failure or fault recovery is detected, the synchronous controller controls the N STS modules 107 to simultaneously issue a grid-connected bidirectional thyristor disconnection instruction or a closing instruction to ensure the control synchronization of the N PCS and STS, and realize the switching of the grid-connected operation of the N power cabinets 101 to the off-grid operation, reducing the impact on the grid-connected and off-grid parallel system, and improving the efficiency and stability of the grid-connected and off-grid mode switching, with high reliability.

[0067] A second aspect of the present invention provides a control method for an on-grid and off-grid parallel system, which is applied to any one of the on-grid and off-grid parallel systems described above, and specifically comprises the following steps:

[0068] Obtaining the actual voltage peak value and the normal voltage peak value output by the municipal power grid when the municipal power grid is in stable power supply at a predetermined monitoring time step, drawing a kurtosis diagram based on the actual voltage peak value and the normal voltage peak value, and detecting and analyzing whether the municipal power grid has a fault through the kurtosis curve of the kurtosis diagram, and if so, controlling the STS module to generate a first opening and closing instruction;

[0069] Based on the first opening and closing instruction, the second bidirectional thyristor at the grid-connected end of the municipal power grid is controlled to be disconnected and the first bidirectional thyristor of the PCS energy storage converter module is controlled to be closed, so that the grid-connected operation is switched to the off-grid operation;

[0070] If the municipal power grid is in a fault state, the real-time voltage peak value of the municipal power grid in the fault state is updated to generate a first peak model diagram, and the non-overlapping peak model area between the first peak model diagram and the second peak model diagram under the normal voltage peak value is calculated and analyzed to see whether it is less than the peak recovery area threshold value. If it is, the STS module is controlled to generate a second opening and closing instruction;

[0071] According to the second opening and closing instruction, the first bidirectional thyristor of the PCS energy storage converter module is controlled to be disconnected and the second bidirectional thyristor of the municipal power grid connected end is controlled to be closed, so that the off-grid operation is switched to the grid-connected operation;

[0072] Obtaining actual power demand of the load end, and obtaining a currently required load end operation mode according to the actual power demand;

[0073] If the load-end operation mode shows that the number of load ends actually required to be operated is N, a group of differential equations is constructed based on the historical sending timestamps when the STS module in each electrical cabinet sends the first opening and closing instructions and the second opening and closing instructions, and the STS modules of the N load ends are coordinated and synchronously controlled by solving the group of differential equations.

[0074] Furthermore, in a preferred embodiment of the present invention, the actual voltage peak value and the normal voltage peak value output by the municipal power grid when the municipal power grid is in a stable power supply at a predetermined monitoring time step are obtained, a kurtosis diagram is drawn based on the actual voltage peak value and the normal voltage peak value, and a kurtosis curve of the kurtosis diagram is used to detect and analyze whether the municipal power grid has a fault. If so, the STS module is controlled to generate a first opening and closing instruction, which specifically includes the following steps:

[0075] Acquire a monitoring strategy of the on-grid and off-grid parallel system for the municipal power grid, and extract a predetermined monitoring time step of the on-grid and off-grid parallel system for the municipal power grid through the monitoring strategy;

[0076] Obtain the normal voltage peak value output by the municipal power grid when the municipal power grid is in a stable power supply at a predetermined monitoring time step through the municipal power grid maintenance log, import multiple normal voltage peak values ​​into the kurtosis diagram for fitting and drawing, and obtain a normal voltage peak kurtosis diagram;

[0077] Obtain several real-time voltage peaks output by the current municipal power grid at a given monitoring time step, construct a kurtosis diagram, import several real-time voltage peaks output at a given monitoring time step into the kurtosis diagram for calculation and fitting, and obtain a real-time voltage peak kurtosis diagram;

[0078] Extracting a kurtosis curve of a normal voltage peak based on the normal voltage peak kurtosis diagram, extracting a kurtosis curve of a real-time voltage peak based on the real-time voltage peak kurtosis diagram, calculating a kurtosis deviation between the kurtosis curve of the normal voltage peak and the kurtosis curve of the real-time voltage peak, and obtaining a kurtosis deviation value;

[0079] An abnormal voltage kurtosis threshold is preset. If the kurtosis deviation value is greater than the abnormal voltage kurtosis threshold, the municipal power grid is calibrated as a fault state, and the STS module is controlled to generate a first opening and closing instruction.

[0080] It should be noted that the system's parallel and off-grid mode switching is usually decided based on whether the municipal power grid is faulty or not. Therefore, it is necessary to perform fault detection on the operation of the municipal power grid. The most significant feature of a municipal power grid fault is the abnormal fluctuation of the voltage peak. Therefore, by detecting and analyzing the voltage peak change, it is possible to determine whether the municipal power grid has a fault, thereby providing a reliable decision-making basis for further switching of the parallel and off-grid system to which mode to execute. The present invention describes the real-time voltage peak change characteristics of the municipal power grid by constructing a kurtosis diagram, and compares and analyzes the normal voltage peak change characteristics of the normal voltage peak output when the municipal power grid is in a stable power supply, that is, calculates whether the kurtosis deviation between the kurtosis curve of the normal voltage peak and the kurtosis curve of the real-time voltage peak is greater than the abnormal voltage kurtosis threshold, wherein the abnormal voltage kurtosis threshold is set to 10% of the normal voltage peak, if the kurtosis deviation is greater than the abnormal voltage kurtosis threshold, it means that the voltage peak change value of the current municipal power grid exceeds 10% of the normal peak, indicating that the municipal power grid voltage output abnormality has produced a fault phenomenon, so the current municipal power grid can be calibrated as a fault state, so that the STS module is required to generate a first opening and closing instruction to control the closing of the first bidirectional thyristor and the disconnection of the second bidirectional thyristor, so as to realize the switching of the grid-connected operation at the load end to the off-grid operation. Through the present invention, it is possible to accurately and efficiently detect and determine whether the municipal power grid is faulty, improve the accuracy and switching efficiency of the grid-connected switching to the off-grid, and greatly reduce the phenomenon of large switching errors of the grid-connected and off-grid control compared to the traditional control method, and the reliability is high.

[0081] Furthermore, in a preferred embodiment of the present invention, if the municipal power grid is in a fault state, the real-time voltage peak value of the municipal power grid in the fault state is updated to generate a first peak model diagram, and the non-overlapping peak model area between the first peak model diagram and the second peak model diagram under the normal voltage peak value is calculated and analyzed to see whether it is less than the peak recovery area threshold value. If it is, the STS module is controlled to generate a second opening and closing instruction, which specifically includes the following steps:

[0082] Under the fault state, the kurtosis curve of the real-time voltage peak of the municipal power grid under the fault state is updated, and a kurtosis model diagram of the real-time voltage peak under the fault state is generated, which is defined as the first peak model diagram;

[0083] Extracting a spike model diagram of a normal voltage peak value in a fault state through a normal voltage peak kurtosis diagram, defining the diagram as a second spike model diagram, and aligning and extracting a non-overlapping spike model region between the first spike model diagram and the second spike model diagram;

[0084] A peak recovery area threshold is preset. If the area value of the non-overlapping peak model area is less than the peak recovery area threshold, the municipal power grid is calibrated as a fault recovery state, and the STS module is controlled to generate a second opening and closing instruction based on the area value.

[0085] It should be noted that when the municipal power grid is maintained and power supply is restored, its voltage peak will gradually return to the normal trend. Therefore, it is necessary to update the peak curve of the voltage peak in real time when the municipal power grid is in a fault state and the load end is in an off-grid state. This can describe in real time whether the abnormal fluctuation of the voltage peak of the municipal power grid has returned to normal or not, thereby further accurately deciding on the switching of the grid-connected mode. The present invention extracts a spike model diagram through an updated kurtosis curve, and the spike model diagram is a peak tip characteristic expression of the voltage peak change trend, which can show the boost recovery status of the municipal power grid voltage peak under a fault state. Therefore, the model diagram is aligned with the spike model diagram of the normal voltage peak under the fault state, and the model diagram area that does not overlap is the deviation part of the real-time voltage peak compared to the normal voltage peak; wherein, the peak recovery area threshold is set to 95% of the normal peak value. If the area value of the non-overlapping peak model area is less than the peak recovery area threshold, it means that the voltage peak change value of the municipal power grid under the fault state has reached 95% of the normal peak value, proving that the municipal power grid has restored normal power supply operation, so the STS module can be further enabled to generate a second opening and closing instruction to control the disconnection of the first bidirectional thyristor and the closing of the second bidirectional thyristor, so that the load end is switched back to grid-connected operation. The present invention can describe and determine the grid-connected fault recovery status of the municipal power grid in the form of peak characteristics, thereby improving the switching accuracy from off-grid to grid-connected, avoiding errors in grid-connected and off-grid mode switching decisions caused by misjudgment of voltage recovery, and effectively ensuring the power supply switching linearity of the grid-connected and off-grid parallel system.

[0086] Furthermore, in a preferred embodiment of the present invention, if the load end operation mode shows that the number of load ends actually required to be operated is N, a differential equation group is constructed according to the historical sending timestamps when the STS module in each electrical cabinet sends the first opening and closing instructions and the second opening and closing instructions, and the STS modules of the N load ends are coordinated and synchronously controlled by solving the differential equation group, which specifically includes the following steps:

[0087] If the load end operation mode shows that the number of load ends actually required to be operated is N, then obtain the historical sending timestamps when the STS module in each electric cabinet sends the first opening and closing instructions and the second opening and closing instructions at the same timing;

[0088] Taking the STS module of each electric cabinet as a control point, the historical sending timestamp of each electric cabinet is interpolated and fitted at the corresponding control point by using the Lagrangian interpolation method to generate a Lagrangian curve;

[0089] Introducing the finite difference method to discretize the Lagrangian curve into a Lagrangian polynomial corresponding to each control point and constructing a differential equation, substituting each Lagrangian polynomial into the differential equation for calculation to obtain a differential equation group;

[0090] Preset the range of equation solutions that allow instantaneous time difference, solve the differential equation group, obtain the instantaneous time difference equation solution of the STS module in each electric cabinet sending the first opening and closing instruction and the second opening and closing instruction, and judge one by one whether the instantaneous time difference equation solution of each electric cabinet is within the range of equation solutions that allow instantaneous time difference;

[0091] If it is, the STS module of the power cabinet is marked as a synchronous transmission STS module, and there is no need to start the synchronous controller for coordinated control;

[0092] If not, the STS module of the power cabinet is marked as an asynchronous sending STS module, and the synchronous controller is started to perform coordinated synchronous control.

[0093] It should be noted that the communication control instructions between the PCS and the STS require extremely strong coordinated control. Therefore, in order to solve this problem, the present invention sets a synchronous controller to ensure the synchronization of the on-grid and off-grid switching of N power cabinets, effectively solves the communication control efficiency problem within the system, and maximizes the control stability of the system and the quality of on-grid and off-grid mode switching. However, the existing on-grid and off-grid control technology has low control decision accuracy for the synchronous controller, making it difficult to achieve low-error synchronous coordinated control of all power cabinets, so that when N power cabinets perform on-grid and off-grid switching, the STS module cannot simultaneously issue the first opening and closing instructions and the second opening and closing instructions to control the opening and closing of the bidirectional thyristor, causing damage and impact to the on-grid and off-grid parallel system. Therefore, this method fits the historical sending timestamps of the STS modules in each power cabinet when sending the opening and closing instructions at the same time sequence into a Lagrangian curve. The Lagrangian curve can express the smoothness of the instantaneous time difference of each STS module sending the opening and closing instructions. Then, the Lagrangian curve is further converted into a group of differential equations for solution. If the solution of the instantaneous time difference equation is within the range of the solution of the equation with the allowed instantaneous time difference, it means that the instantaneous time difference of sending the opening and closing instructions between the STS modules of the N power cabinets is within the allowed instantaneous time difference interval, so there is no need to start the synchronous controller for coordinated control; otherwise, it means that the instantaneous time difference of sending the opening and closing instructions between the N STS modules has deviated from the allowed instantaneous time difference interval, and some STS modules may not be able to send the opening and closing instructions synchronously, so it is necessary to start the synchronous controller for synchronous and coordinated control so that the instantaneous time difference between the two can be corrected. The present invention can achieve the synchronous control effect of the STS module when N power cabinets are switched on and off the grid, reduce the impact on the on-grid and off-grid parallel system, improve the stability and safety of on-grid and off-grid switching of multiple power cabinets, and ensure the service life of the on-grid and off-grid parallel system.

[0094] The above is based on the ideal embodiment of the present invention, and its description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A control method for an on-grid and off-grid parallel system, characterized in that: The on-grid and off-grid parallel system comprises a backup power supply end, and the backup power supply end is equipped with an electric cabinet: The number of the electric cabinets is N, and each of the electric cabinets is provided with a plurality of battery modules, the plurality of battery modules are connected to a control box through insulating cables, and the control box is pre-charged and grid-connected to a PCS energy storage converter module; The PCS energy storage converter module is connected to the backup power supply end of one STS module, and the main power supply end of another STS module is connected to the municipal power grid, and the output end of the municipal power grid in the STS module and the output end of the PCS energy storage converter module are connected to the load end, so that the grid connection and off-grid connection can be seamlessly switched; The grid-end input interface of each of the electric cabinets is connected to the grid combiner cabinet after passing through the STS module. An EPS load combiner cabinet is arranged next to the grid combiner cabinet. The EPS load combiner cabinet is connected to the load-end output interface of each of the electric cabinets through an insulated cable. The distances between the N electric cabinets and the power grid combiner cabinet and the EPS load combiner cabinet are not uniform, and the length difference of the insulated cables connecting the power grid end and the load end of each electric cabinet to the power grid combiner cabinet and the EPS load combiner cabinet does not exceed 5%; The control method comprises the following steps: Obtaining the actual voltage peak value and the normal voltage peak value output by the municipal power grid when the municipal power grid is in stable power supply at a predetermined monitoring time step, drawing a kurtosis diagram based on the actual voltage peak value and the normal voltage peak value, and detecting and analyzing whether the municipal power grid has a fault through the kurtosis curve of the kurtosis diagram, and if so, controlling the STS module to generate a first opening and closing instruction; Based on the first opening and closing instruction, the second bidirectional thyristor at the grid-connected end of the municipal power grid is controlled to be disconnected and the first bidirectional thyristor of the PCS energy storage converter module is controlled to be closed, so that the grid-connected operation is switched to the off-grid operation; If the municipal power grid is in a fault state, the real-time voltage peak value of the municipal power grid in the fault state is updated to generate a first peak model diagram, and the non-overlapping peak model area between the first peak model diagram and the second peak model diagram under the normal voltage peak value is calculated and analyzed to see whether it is less than the peak recovery area threshold value. If it is, the STS module is controlled to generate a second opening and closing instruction; According to the second opening and closing instruction, the first bidirectional thyristor of the PCS energy storage converter module is controlled to be disconnected and the second bidirectional thyristor of the municipal power grid connected end is controlled to be closed, so that the off-grid operation is switched to the grid-connected operation; Obtaining actual power demand of the load end, and obtaining a currently required load end operation mode according to the actual power demand; If the load end operation mode shows that the number of load ends actually required to be operated is N, a differential equation group is constructed according to the historical sending timestamps when the STS module in each power cabinet sends the first opening and closing instructions and the second opening and closing instructions, and the STS modules of the N load ends are coordinated and synchronously controlled by solving the differential equation group; The actual voltage peak value and the normal voltage peak value output by the municipal power grid when the municipal power grid is in a stable power supply at a predetermined monitoring time step are obtained, a kurtosis diagram is drawn based on the actual voltage peak value and the normal voltage peak value, and the kurtosis curve of the kurtosis diagram is used to detect and analyze whether the municipal power grid has a fault. If so, the STS module is controlled to generate a first opening and closing instruction, which specifically includes the following steps: Acquire a monitoring strategy of the on-grid and off-grid parallel system for the municipal power grid, and extract a predetermined monitoring time step of the on-grid and off-grid parallel system for the municipal power grid through the monitoring strategy; Obtain the normal voltage peak value output by the municipal power grid when the municipal power grid is in a stable power supply at a predetermined monitoring time step through the municipal power grid maintenance log, import multiple normal voltage peak values ​​into the kurtosis diagram for fitting and drawing, and obtain a normal voltage peak kurtosis diagram; Obtain several real-time voltage peaks output by the current municipal power grid at a given monitoring time step, construct a kurtosis diagram, import several real-time voltage peaks output at a given monitoring time step into the kurtosis diagram for calculation and fitting, and obtain a real-time voltage peak kurtosis diagram; Extracting a kurtosis curve of a normal voltage peak based on the normal voltage peak kurtosis diagram, extracting a kurtosis curve of a real-time voltage peak based on the real-time voltage peak kurtosis diagram, calculating a kurtosis deviation between the kurtosis curve of the normal voltage peak and the kurtosis curve of the real-time voltage peak, and obtaining a kurtosis deviation value; An abnormal voltage kurtosis threshold is preset. If the kurtosis deviation value is greater than the abnormal voltage kurtosis threshold, the municipal power grid is calibrated as a fault state, and the STS module is controlled to generate a first opening and closing instruction.

2. The control method of the on-grid and off-grid parallel system according to claim 1, characterized in that: The PCS energy storage converter module includes a soft start loop, a grid-connected relay is provided in the soft start loop, and the soft start loop is connected to the STS module via the grid-connected relay.

3. The control method of the on-grid and off-grid parallel system according to claim 2, characterized in that: The grid-connected relay is connected to the loop outlet of the AC filter loop, and the loop inlet of the AC filter loop is connected to the bidirectional inverter unit.

4. The control method of the on-grid and off-grid parallel system according to claim 3, characterized in that: The bidirectional inverter unit is arranged in a soft-start circuit, and the soft-start circuit is connected to an AC lightning protection module through an insulating cable.

5. The control method of the on-grid and off-grid parallel system according to claim 1, characterized in that: The STS module comprises an STS static switching switch, a plurality of first bidirectional thyristors are arranged inside the STS static switching switch, and the plurality of first bidirectional thyristors are connected to the PCS energy storage converter module.

6. The control method of the on-grid and off-grid parallel system according to claim 5, characterized in that: The STS static switching switch is internally provided with a plurality of second bidirectional thyristors, and the plurality of second bidirectional thyristors are connected to the grid-connected end of the municipal power grid.

7. The control method of the on-grid and off-grid parallel system according to claim 1, characterized in that: If the municipal power grid is in a fault state, the real-time voltage peak value of the municipal power grid in the fault state is updated to generate a first peak model diagram, and the non-overlapping peak model area between the first peak model diagram and the second peak model diagram under the normal voltage peak value is calculated and analyzed to see whether it is less than the peak recovery area threshold value. If it is less than, the STS module is controlled to generate a second opening and closing instruction, which specifically includes the following steps: Under the fault state, the kurtosis curve of the real-time voltage peak value of the municipal power grid under the fault state is updated, and a kurtosis model diagram of the real-time voltage peak value under the fault state is generated, which is defined as the first peak model diagram; Extracting a spike model diagram of a normal voltage peak value in a fault state through a normal voltage peak kurtosis diagram, defining the diagram as a second spike model diagram, and aligning and extracting a non-overlapping spike model region between the first spike model diagram and the second spike model diagram; A peak recovery area threshold is preset. If the area value of the non-overlapping peak model area is less than the peak recovery area threshold, the municipal power grid is calibrated as a fault recovery state, and the STS module is controlled to generate a second opening and closing instruction based on the area value.

8. The control method of the on-grid and off-grid parallel system according to claim 1, characterized in that: If the load end operation mode shows that the number of load ends actually required to be operated is N, a differential equation group is constructed according to the historical sending timestamps when the STS module in each electric cabinet sends the first opening and closing instructions and the second opening and closing instructions, and the STS modules of the N load ends are coordinated and synchronously controlled by solving the differential equation group, which specifically includes the following steps: If the load end operation mode shows that the number of load ends actually required to be operated is N, then obtain the historical sending timestamps when the STS module in each electric cabinet sends the first opening and closing instructions and the second opening and closing instructions at the same timing; Taking the STS module of each electric cabinet as a control point, the historical sending timestamp of each electric cabinet is interpolated and fitted at the corresponding control point by using the Lagrangian interpolation method to generate a Lagrangian curve; Introducing the finite difference method to discretize the Lagrangian curve into a Lagrangian polynomial corresponding to each control point and constructing a differential equation, substituting each Lagrangian polynomial into the differential equation for calculation to obtain a differential equation group; Preset the range of equation solutions that allow instantaneous time difference, solve the differential equation group, obtain the instantaneous time difference equation solution of the STS module in each electric cabinet sending the first opening and closing instruction and the second opening and closing instruction, and judge one by one whether the instantaneous time difference equation solution of each electric cabinet is within the range of equation solutions that allow instantaneous time difference; If it is, the STS module of the power cabinet is marked as a synchronous transmission STS module, and there is no need to start the synchronous controller for coordinated control; If not, the STS module of the power cabinet is marked as an asynchronous sending STS module, and the synchronous controller is started to perform coordinated synchronous control.

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