Coordinated control method and system for off-grid system with grid-connected energy storage

Abstract

A coordinated control method and system for off-grid operation of a system containing grid-type energy storage determines a state of charge threshold for starting a diesel generator and a state of charge threshold for shutting down the diesel generator; when the net load power is greater than zero and , the grid-type energy storage sends a signal to the master station to start the diesel generator; when , the grid-type energy storage sends a signal to the master station to shut down the diesel generator; when the net load power is greater than zero and , if the discharge power of the grid-type energy storage in a discharging state is greater than the net load power, the grid-type energy storage discharges to meet the net load power; if the discharge power of the grid-type energy storage in a discharging state is not greater than the net load power, the grid-type energy storage sends a signal to the master station to start the diesel generator, and the diesel generator and the grid-type energy storage operate jointly to meet the net load power, thereby achieving coordinated control of off-grid operation of the system.

Description

Technical Field

[0001] The present invention belongs to the field of source-grid-load-storage coordinated control strategy, and in particular, relates to a method and system for coordinated control of off-grid operation of a system containing grid-type energy storage. Background Art

[0002] In the grid-connected operation mode, the system can reasonably arrange the output of distributed power sources according to the control and dispatch requirements of the power grid; in the off-grid mode, one power source is usually selected as the main power source of the system to provide voltage and frequency support, such as energy storage or diesel generators. Diesel generators have high power generation costs and minimum operating power limits, which are not economical and environmentally friendly. They are used as backup main power sources in most scenarios. The off-grid system selects energy storage as the main power source. When the system switches from grid-connected to off-grid, the energy storage switches from the PQ control mode to the voltage-frequency (VF) mode. Wind turbines, photovoltaics, diesel generators and other power sources work together with energy storage to provide energy for the load. However, there are two problems in this scenario. On the one hand, when the system is unplanned off-grid, the switching of the energy storage mode depends on the accuracy of the island judgment, and the system voltage fluctuates greatly during the switching process, which may cause the energy storage mode to switch unsmoothly or fail; on the other hand, after the system is successfully off-grid, when the VF-controlled energy storage and the diesel generator are running in parallel, if the system is disturbed, the voltage deviation of the two ports will cause a large reactive circulating current, which may cause the overcurrent protection of the energy storage converter to operate, and the diesel generator bears the power of all loads, and the system may collapse. [1] .

[0003] The application of grid-type energy storage is a hot topic at present. It adopts control similar to that of synchronous motors, can provide inertia and voltage support, can operate in both grid-connected and off-grid states, and can enhance the stability of the system. When the system is in off-grid mode, the grid-type energy storage is used as the main power source. When the energy storage charge state is low or the output is insufficient and cannot meet the load demand, the diesel generator is turned on to output. The diesel generator has a slow ramp rate and cannot provide power to the system immediately, resulting in large frequency fluctuations. The grid-type energy storage can stabilize the system through its own natural frequency response process. In summary, the grid-type energy storage is a better choice for the main power source of the off-grid system. It not only avoids the stability problems caused by the switching of control modes when off-grid, but also provides strong support when the output or load of other power sources fluctuates, and maintains the stability of the parallel operation of multiple power systems. However, there is a lack of exploration of source-load coordinated control strategies for grid-type energy storage as the main power source in off-grid systems. Therefore, it is urgent to design and formulate off-grid system coordinated control strategies with grid-type energy storage as the main power source to reduce the impact of disturbances on system stability and maintain system power balance. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention provides a coordinated control method and system for off-grid operation of a system containing grid-connected energy storage, which maintains system power balance and enhances system stability. The strategy is applicable to the off-grid operation mode of the system, wherein the grid-connected energy storage serves as the main power source to provide frequency and voltage support for the system, and both wind and light adopt constant power control. The backup power source is a diesel generator, which adopts a synchronous machine control mode. The initial state is closed, and the grid-connected switch is closed when the access condition is triggered, and the system is connected after synchronization.

[0005] The present invention adopts the following technical solution.

[0006] The present invention proposes a coordinated control method for off-grid operation of a system containing grid-connected energy storage, taking the difference between the load power and the output power of a wind turbine generator set and the output power of a photovoltaic generator set as the net load power; comprising:

[0007] Obtain the real-time state of charge, charge and discharge rate, and charge and discharge ratio of the grid-type energy storage, and obtain the maximum output power and minimum output power of the diesel generator set;

[0008] Based on the output power change curve of the diesel generator set during the startup phase, determine the startup time required for the diesel generator set to reach the output power command value after it is started; based on the output power change curve of the diesel generator set during the shutdown phase, determine the shutdown time required for the diesel generator set to reach zero output power after it is shut down;

[0009] The state of charge threshold for starting the diesel generator and the state of charge threshold for shutting down the diesel generator are determined by the following relationship:

[0010] ,

[0011] In the formula, is the charge state threshold for starting the diesel generator, is the charge state threshold for shutting down the diesel generator, and are the upper and lower limits of the state of charge of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, It is the start-up time required for the diesel generator set to reach the output power command value after it is turned on. It is the shutdown time required for the diesel generator set to output zero power after shutdown. is the state of charge margin value based on control delay and signal transmission delay;

[0012] Real-time monitoring of the charge state of grid-connected energy storage;

[0013] When the net load power is greater than zero and When the grid-connected energy storage sends a signal to the master station to start the diesel generator, the master station obtains the status signal of the diesel generator grid-connected circuit breaker and generates the diesel generator start-up command and output power command value;

[0014] when When the grid-connected energy storage sends a signal to the master station to shut down the diesel generator, the master station obtains the status signal of the diesel generator grid-connected circuit breaker and generates a shutdown command for the diesel generator;

[0015] When the net load power is greater than zero and When the discharge power of the grid-forming energy storage in the discharging state is greater than the net load power, the grid-forming energy storage discharges to meet the net load power; if the discharge power of the grid-forming energy storage in the discharging state is not greater than the net load power, the grid-forming energy storage sends a signal to the master station to start the diesel generator, and the diesel generator and the grid-forming energy storage operate together to meet the net load power.

[0016] Preferably, the rated parameters of the grid-connected energy storage and the diesel generator are used to determine the state of charge threshold for starting the diesel generator and the state of charge threshold for shutting down the diesel generator corresponding to the start time of the coordinated control of off-grid operation of the system.

[0017] Preferably, when the net load power is greater than zero and When the diesel generator is started,

[0018] If the net load power is less than the minimum output power of the diesel generator, the minimum output power of the diesel generator is used as the output power command value of the diesel generator, and the grid-type energy storage is charged with the difference between the minimum output power of the diesel generator and the net load power;

[0019] If the net load power is not less than the minimum output power of the diesel generator and less than the maximum output power of the diesel generator, the net load power is used as the output power command value of the diesel generator; when load disturbance or wind and solar power output fluctuation occurs in the system, the power shortage or surplus in the system is supplemented or absorbed by the grid-connected energy storage;

[0020] If the net load power is greater than the maximum output power of the diesel generator, the maximum output power of the diesel generator will be used as the output power command value of the diesel generator, and the grid-type energy storage will be discharged to meet the shortfall of the net load power; if the grid-type energy storage discharge power cannot meet the shortfall of the net load power, the loads will be cut off in order from low to high in terms of their importance.

[0021] Preferably, when the net load power is less than zero and When the grid-connected energy storage is charged, it is charged with the absolute value of the net load power.

[0022] Preferably, after shutting down the diesel generator, if the net load power is greater than zero, the grid-type energy storage is discharged to meet the net load power; if the discharge power of the grid-type energy storage cannot meet the shortfall of the net load power, the loads are cut off in order of importance from low to high; after shutting down the diesel generator, if the net load power is less than zero, when the absolute value of the net load power is greater than the maximum charging power of the grid-type energy storage, the grid-type energy storage is charged with the absolute value of the net load power; if the absolute value of the net load power is not greater than the maximum charging power of the grid-type energy storage, the grid-type energy storage is charged with the maximum charging power.

[0023] Preferably, the diesel generator and the grid-connected energy storage are operated in combination to meet the net load power, including:

[0024] Start the diesel generator, and the output power command value of the diesel generator is the minimum output power; when the real-time charge state of the grid-type energy storage is less than Before and / or the running time of the diesel generator is not less than the operating limit, the master station adjusts the wind and solar output to meet the net load power shortage. If the net load power shortage cannot be met after adjusting the wind and solar output, the loads are cut in order from low to high in importance.

[0025] Preferably, when the net load power is less than zero and When the grid-connected energy storage is charged, it is charged with the absolute value of the net load power.

[0026] Preferably, when the running time of the diesel generator is greater than the running limit, the diesel generator sends a shutdown request signal to the master station; if the net load power is greater than zero, the master station controls the grid-type energy storage to use the output power command value before the diesel generator stops operating as the discharge power command to meet the net load power; if the net load power is less than zero and , the grid-type energy storage is charged with the absolute value of the net load power; if the net load power is less than zero and , the grid-type energy storage stops charging, and the master station controls the abandonment of wind power first and then solar power.

[0027] Preferably, the diesel generator comprises: a speed governor, a diesel prime mover and a synchronous generator;

[0028] The speed regulator corrects the speed of the diesel engine according to the difference between the grid angular frequency setting value and the actual value of the angular frequency to output the actual value of the control torque;

[0029] According to the actual value of the angular frequency, the difference between the actual value of the control torque and the set value of the control torque is compensated to obtain the control torque;

[0030] The synchronous generator outputs a power command value driven by the control torque;

[0031] Among them, the control torque setting value satisfies the following relationship:

[0032] ,

[0033] In the formula, is the control torque setting value, is the output power command value of the diesel generator, is the rated speed of the diesel generator.

[0034] The present invention also proposes a system off-grid operation coordination control system including grid-type energy storage, which takes the difference between load power and the output power of wind turbine generator set and the output power of photovoltaic generator set as the net load power; including:

[0035] The acquisition module is used to obtain the real-time state of charge, charge and discharge rate, and charge and discharge ratio of the grid-type energy storage, and obtain the maximum output power and minimum output power of the diesel generator set;

[0036] The threshold setting module is used to determine the starting time required for the diesel generator set to reach the output power command value after it is turned on based on the output power change curve of the diesel generator set in the starting stage; determine the shutdown time required for the diesel generator set to output zero after it is shut down based on the output power change curve of the diesel generator set in the shutdown stage; and determine the charge state threshold for starting the diesel generator and the charge state threshold for shutting down the diesel generator respectively according to the following relationship:

[0037] ,

[0038] In the formula, is the charge state threshold for starting the diesel generator, is the charge state threshold for shutting down the diesel generator, and are the upper and lower limits of the state of charge of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, It is the start-up time required for the diesel generator set to reach the output power command value after it is turned on. It is the shutdown time required for the diesel generator set to output zero power after shutdown. is the state of charge margin value based on control delay and signal transmission delay;

[0039] The coordination control module is used to monitor the charging state of the grid-type energy storage in real time; when the net load power is greater than zero and When , the grid-type energy storage sends a signal to the master station to start the diesel generator. The master station obtains the status signal of the diesel generator grid-connected circuit breaker and generates the diesel generator start-up instruction and output power instruction value; when When the net load power is greater than zero and When the discharge power of the grid-forming energy storage in the discharging state is greater than the net load power, the grid-forming energy storage discharges to meet the net load power; if the discharge power of the grid-forming energy storage in the discharging state is not greater than the net load power, the grid-forming energy storage sends a signal to the master station to start the diesel generator, and the diesel generator and the grid-forming energy storage operate together to meet the net load power.

[0040] The beneficial effects of the present invention are that, compared with the prior art, at least the following are included: in the off-grid operation coordinated control method of a system containing grid-type energy storage proposed in the present invention, the grid-type energy storage is used as the main power source in the off-grid system, and the real-time charge state and charge-discharge state of the grid-type energy storage are used to generate a control signal for starting or shutting down the diesel generator, thereby formulating a coordinated control strategy for wind, light, diesel and storage under different grid-type energy storage charge state scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the improved control block diagram of the diesel generator proposed by the present invention;

[0042] Figure 2 A relationship curve between the output power command value and the output power measurement value of the grid-type energy storage obtained by coordinated control using the method proposed by the present invention;

[0043] Figure 3 The graph is a relationship curve between the output power command value and the output power measurement value of the diesel generator obtained by coordinated control using the method proposed by the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0045] The present invention proposes a coordinated control method for off-grid operation of a system with grid-connected energy storage, which first obtains the output power of a wind turbine generator set, the output power of a photovoltaic generator set, and the load power, and then uses the difference between the load power and the output power of the wind turbine generator set and the output power of the photovoltaic generator set as the net load power; including:

[0046] Step 1: Obtain the real-time state of charge, charge and discharge rate, and charge and discharge ratio of the grid-type energy storage, and obtain the maximum output power and minimum output power of the diesel generator.

[0047] The charge and discharge rate C is used to indicate the battery charge and discharge capacity rate. Charge and discharge rate = charge and discharge current / rated capacity. For example, when a battery with a rated capacity of 100A is discharged at 50A, its discharge rate is 0.5C. 1C, 2C, and 0.5C are battery discharge rates, which are a measure of discharge speed. If the capacity is discharged in 1 hour, it is called 1C discharge; if it is discharged in 2 hours, it is called 1 / 2=0.5C discharge. Generally, the capacity of the battery can be detected by different discharge currents. For a 24Ah battery, the 1C discharge current is 24A, and the 0.5C discharge current is 12A. The larger the discharge current, the shorter the discharge time.

[0048] In the embodiment, the minimum output power of the diesel generator The maximum output power of the diesel generator 0.3 times of ;

[0049] Net load power has the volatility and uncertainty of load demand and new energy output. When the net load power is greater than zero, the maximum wind and solar output is taken as the optimization goal, and the discharge power of the grid-type energy storage and the output power of the diesel generator are regulated; when the net load power is less than zero, the maximum wind and solar output is taken as the optimization goal, and the charging power of the grid-type energy storage is regulated.

[0050] The real-time state of charge of the grid-connected energy storage meets the constraints: ,in and are the upper and lower limits of the state of charge of the grid-type energy storage, It is the real-time charge status of grid-type energy storage.

[0051] Step 2: Based on the output power change curve of the diesel generator during the startup phase, determine the startup time required for the diesel generator to reach the output power command value after it is started; based on the output power change curve of the diesel generator set during the shutdown phase, determine the shutdown time required for the diesel generator set to have zero output power after it is shut down; and determine the charge state threshold for starting the diesel generator and the charge state threshold for shutting down the diesel generator.

[0052] Specifically, the start-up time includes: the start-up time required for the diesel generator to reach the minimum output power after it is turned on; the start-up time required for the diesel generator to reach the maximum output power after it is turned on; the start-up time required for the diesel generator to reach the net load power after it is turned on;

[0053] The state of charge threshold for starting the diesel generator is determined by the following relationship:

[0054] ,

[0055] In the formula, is the charge state threshold for starting the diesel generator, is the lower limit of the state of charge of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, It is the start-up time required for the diesel generator set to reach the output power command value after it is turned on. is the state of charge margin value based on control delay and signal transmission delay;

[0056] The state of charge threshold for shutting down the diesel generator is determined by the following relationship:

[0057] ,

[0058] In the formula, is the charge state threshold for shutting down the diesel generator, is the upper limit of the state of charge of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, It is the shutdown time required for the diesel generator set to output zero power after shutdown. is the state of charge margin value based on control delay and signal transmission delay;

[0059] Step 3: real-time monitoring of the state of charge of the grid-connected energy storage;

[0060] When the net load power is greater than zero and When the grid-connected energy storage sends a signal to the master station to start the diesel generator, the master station obtains the status signal of the diesel generator grid-connected circuit breaker and generates the diesel generator start-up command and output power command value;

[0061] when When the grid-connected energy storage sends a signal to the master station to shut down the diesel generator, the master station obtains the status signal of the diesel generator grid-connected circuit breaker and generates a shutdown command for the diesel generator;

[0062] When the net load power is greater than zero and When the discharge power of the grid-forming energy storage in the discharging state is greater than the net load power, the grid-forming energy storage discharges to meet the net load power; if the discharge power of the grid-forming energy storage in the discharging state is not greater than the net load power, the grid-forming energy storage sends a signal to the master station to start the diesel generator, and the diesel generator and the grid-forming energy storage operate together to meet the net load power.

[0063] In the off-grid operation coordinated control method of a system containing grid-type energy storage proposed in the present invention, by setting the charge state threshold for starting the diesel generator and the charge state threshold for shutting down the diesel generator, the grid-type energy storage is used as the main power supply of the off-grid system, and the control signal for starting or shutting down the diesel generator is generated by the real-time charge state and charging and discharging state of the grid-type energy storage; it takes a period of time for the diesel generator to reach the output power command value after it is started, and it also takes a period of time for the output power to be zero after it is shut down. During this period of time, the energy storage power station continues to discharge or charge, and there is a possibility of breaking through the lower limit or upper limit of the charge state, which poses a hidden danger to safe operation. Therefore, by setting the charge state threshold for starting the diesel generator and the charge state threshold for shutting down the diesel generator, not only the safety and service life of the charging and discharging of the grid-type energy storage are guaranteed, but it is also beneficial to give priority to the output of new energy such as wind, solar and storage in the off-grid system and reduce the output of the diesel generator, thereby improving the economy.

[0064] Specifically, the rated parameters of the grid-connected energy storage and the diesel generator are used to determine the state of charge threshold for starting the diesel generator and the state of charge threshold for shutting down the diesel generator corresponding to the start time of the off-grid operation coordinated control of the system.

[0065] Specifically, the state of charge of the grid-type energy storage is monitored in real time. When the net load power is greater than zero and When the grid-connected energy storage sends a signal to the master station to start the diesel generator, the master station obtains the status signal of the diesel generator grid-connected circuit breaker and generates the diesel generator start-up instruction and output power instruction value, including:

[0066] 1) Start the diesel generator. If the net load power is less than the minimum output power of the diesel generator, the minimum output power of the diesel generator is used as the output power instruction value of the diesel generator. Under this instruction, the excess output power of the diesel generator after the output meets the net load power demand is used to charge the grid-connected energy storage;

[0067] In the embodiment, In the scenario of, when the net load power is less than the minimum output power of the diesel generator, the output power command value of the diesel generator The minimum output power , at this time the grid-type energy storage changes to the charging state, and the charging power The minimum output power of the diesel generator Net load power The difference between the charge state threshold value set for starting the diesel generator is greater than But the margin is not much, so in In the scenario where the net load power is less than the minimum output power of the diesel generator, the diesel generator is started first to ensure that the grid-forming energy storage is in a safe discharge state, which protects the grid-forming energy storage. At the same time, the surplus output power of the diesel generator can also charge the grid-forming energy storage.

[0068] 2) Start the diesel generator. If the net load power is not less than the minimum output power of the diesel generator and less than the maximum output power of the diesel generator, the net load power is used as the output power command value of the diesel generator. Under this command, the output of the diesel generator can meet the net load power demand.

[0069] In the embodiment, when the net load power is not less than the minimum output power of the diesel generator and less than the maximum output power of the diesel generator, the output power command value of the diesel generator Net load power At this time, the control optimization goal is to reduce the number of diesel generator starts and stops. The diesel generator still gives priority to meeting the net load power, and the grid-type energy storage does not contribute. In the scenario of power grid-connected energy storage, since the grid-connected energy storage has the ability to discharge and charge, when load disturbance or output fluctuation occurs in the system, the power shortage or surplus in the system is supplemented or absorbed by the grid-connected energy storage, which fully utilizes the frequency support capability of the grid-connected energy storage and avoids the adjustment of the output power of the diesel generator, which is conducive to improving the stability and reliability of the system.

[0070] 3) Start the diesel generator. If the net load power is greater than the maximum output power of the diesel generator, the maximum output power is used as the output power command value of the diesel generator, and the grid-type energy storage is discharged to meet the net load power shortage. Under this command, the diesel generator runs at full power, and the net load power shortage is met by the grid-type energy storage discharge power. If the grid-type energy storage discharge power cannot meet the net load power shortage, the loads are cut off in order of importance from low to high.

[0071] In the embodiment, when the net load power is greater than the maximum output power of the diesel generator, the output power command value of the diesel generator The maximum output power is , grid-type energy storage discharge to meet the net load power shortage ,exist In the scenario of grid-type energy storage, the discharge output is limited. When the real-time charge state of the grid-type energy storage is less than Previously, the master station needed to adjust the wind and solar power output in a timely manner to adjust the net load power balance. If the net load power balance could not be achieved after adjusting the wind and solar power output, the loads would be cut in order from low to high in importance to ensure system stability.

[0072] In the above control process, although direct control of wind and solar power output is not involved, diesel generator output power instructions and grid-connected energy storage instructions are generated with net load power as the response target. In load power response scenarios, a coordinated control strategy of wind, solar, diesel and storage is implemented to support the safety and reliability of the system's off-grid operation.

[0073] Real-time monitoring of the charging status of grid-type energy storage. When the net load power is less than zero and When the grid-connected energy storage is charged, it is charged with the absolute value of the net load power.

[0074] Specifically, real-time monitoring of the state of charge of the grid-type energy storage When the grid-connected energy storage sends a signal to the master station to shut down the diesel generator, the master station obtains the status signal of the diesel generator grid-connected circuit breaker and generates a shutdown command for the diesel generator, including:

[0075] After shutting down the diesel generator, if the net load power is greater than zero, the grid-type energy storage discharges to meet the net load power. If the grid-type energy storage discharge power cannot meet the net load power shortfall, the loads are cut off in order of importance from low to high. After shutting down the diesel generator, if the net load power is less than zero, when the absolute value of the net load power is greater than the maximum charging power of the grid-type energy storage, the grid-type energy storage is charged with the absolute value of the net load power. If the absolute value of the net load power is not greater than the maximum charging power of the grid-type energy storage, the grid-type energy storage is charged with the maximum charging power, forming a The wind, solar and storage coordinated control strategy based on load demand fluctuations and wind and solar output fluctuations in the scenario has improved the new energy absorption rate and brought into play the voltage support capacity of grid-connected energy storage.

[0076] Specifically, when the net load power is greater than zero and When the discharge power of the grid-type energy storage in the discharge state is greater than the net load power, the grid-type energy storage discharges to meet the net load power, achieving The wind-solar-storage coordinated control strategy in this scenario uses the voltage support and frequency support capabilities of the grid-connected energy storage to achieve stable off-grid operation of the system, while reducing the start and stop of diesel generators while ensuring the absorption rate of new energy. If the discharge power of the grid-connected energy storage in the discharge state is not greater than the net load power, the grid-connected energy storage sends a signal to the master station to start the diesel generator, and the diesel generator and the grid-connected energy storage work together to meet the net load power. The wind, solar, energy storage and diesel coordinated control strategy in this scenario uses the voltage and frequency support capabilities of grid-connected energy storage to achieve stable off-grid operation of the system;

[0077] Furthermore, the diesel generator and grid-connected energy storage are operated together to meet the net load power, including:

[0078] Start the diesel generator, the output power command value of the diesel generator The minimum output power ,

[0079] When the diesel generator and grid-connected energy storage are operated together, the real-time state of charge of the grid-connected energy storage is less than Before and / or the running time of the diesel generator is not less than the operating limit, the master station needs to adjust the wind and solar output in time to make up for the power shortage. If the power shortage cannot be met after adjusting the wind and solar output, the loads will be cut in order from low to high in order of importance to ensure system stability.

[0080] When the net load power is less than zero and When the grid-connected energy storage is charged, it is charged with the absolute value of the net load power.

[0081] When the running time of the diesel generator is greater than the running limit, the diesel generator sends a shutdown request signal to the master station; if the net load power is greater than zero, the master station controls the grid-type energy storage to use the output power command value before the diesel generator stops operating as the discharge power command to meet the net load power; if the net load power is less than zero and , the grid-type energy storage is charged with the absolute value of the net load power; if the net load power is less than zero and , the grid-type energy storage stops charging, and the master station controls the abandonment of wind power first and then solar power.

[0082] Diesel generators generally adjust their output power by responding to changes in system frequency. When a load disturbance occurs in the system, due to the inertial support of the grid-type energy storage, the frequency change sensed by the diesel generator is not obvious, and the output power is adjusted slowly. At this time, the power gap in the system is temporarily supplemented by the energy storage. After the diesel generator power stabilizes, the energy storage and system power stabilize. In order to improve the power response speed of the diesel generator and make the system reach a stable state more quickly, the control method of the diesel generator is improved. The improved control system is as follows: Figure 1 As shown. The diesel generator includes: a speed governor, a diesel prime mover and a synchronous generator; wherein the speed governor is an automatic regulating device, which automatically increases or decreases the fuel supply of the injection pump according to the change of the diesel engine load, so that the diesel engine can run at a stable speed. The speed governor corrects the speed of the diesel prime mover according to the difference between the angular frequency setting value and the actual angular frequency value of the power grid to output the actual value of the control torque, and compensates the difference between the actual value of the control torque and the control torque setting value according to the actual value of the angular frequency to obtain the control torque , in the control torque The synchronous generator output power command value under the drive of ; wherein the control torque setting value satisfies the following relationship:

[0083] ,

[0084] In the formula, is the control torque setting value, is the output power command value of the diesel generator, is the rated speed of the diesel generator;

[0085] Through the improvement of the above control method, the response rate of the diesel generator is improved, the startup time and shutdown time are shortened, which is equivalent to improving the operation time. The probability of the scenario, in which the grid-connected energy storage discharge has a high priority, further highlighting the status of the grid-connected energy storage as the main power source in the off-grid operation of the system.

[0086] The method proposed in the present invention is simulated in MATLAB. When T=5s, the method proposed in the present invention is implemented on the grid-type energy storage and the diesel generator; Figure 2 In the figure, the solid line is the output power measurement value of the grid-type energy storage, and the dotted line with a circle is the output power command value of the grid-type energy storage. The grid-type energy storage gives a correct and rapid response; Figure 3 In the figure, the solid line is the output power command value of the diesel generator, and the dotted line with a circle is the output power command value of the diesel generator. The diesel generator gives a correct and rapid response; and combined with Figure 2 and Figure 3 It can be seen that the diesel and energy storage can achieve power balance quickly. The safety margin of the energy storage charge state is taken into account when setting the boundary conditions for starting and stopping the diesel generator. When the energy storage reaches a certain value before the lower limit of the charge state, the diesel generator is turned on. During the process of the diesel generator power gradually reaching the set value, the safety of the energy storage charge state and discharge activities is guaranteed. At the same time, the minimum operating power and minimum operating time of the diesel generator are set to ensure the economy of the diesel generator operation. In view of the fact that the diesel generator adjusts the power slowly and causes the system to take a long time to reach stability, the control strategy of the diesel generator is improved to shorten the time for the system to reach power balance.

[0087] The present invention also proposes a system off-grid operation coordination control system including grid-type energy storage, which takes the difference between load power and the output power of wind turbine generator set and the output power of photovoltaic generator set as the net load power; including:

[0088] The acquisition module is used to obtain the real-time state of charge, charge and discharge rate, and charge and discharge ratio of the grid-type energy storage, and obtain the maximum output power and minimum output power of the diesel generator set;

[0089] The threshold setting module is used to determine the starting time required for the diesel generator set to reach the output power command value after it is turned on based on the output power change curve of the diesel generator set in the starting stage; determine the shutdown time required for the diesel generator set to output zero after it is shut down based on the output power change curve of the diesel generator set in the shutdown stage; and determine the charge state threshold for starting the diesel generator and the charge state threshold for shutting down the diesel generator respectively according to the following relationship:

[0090] ,

[0091] In the formula, is the charge state threshold for starting the diesel generator, is the charge state threshold for shutting down the diesel generator, and are the upper and lower limits of the state of charge of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, It is the start-up time required for the diesel generator set to reach the output power command value after it is turned on. It is the shutdown time required for the diesel generator set to output zero power after shutdown. is the state of charge margin value based on control delay and signal transmission delay;

[0092] The coordination control module is used to monitor the charging state of the grid-type energy storage in real time; when the net load power is greater than zero and When , the grid-type energy storage sends a signal to the master station to start the diesel generator. The master station obtains the status signal of the diesel generator grid-connected circuit breaker and generates the diesel generator start-up instruction and output power instruction value; when When the net load power is greater than zero and When the discharge power of the grid-forming energy storage in the discharging state is greater than the net load power, the grid-forming energy storage discharges to meet the net load power; if the discharge power of the grid-forming energy storage in the discharging state is not greater than the net load power, the grid-forming energy storage sends a signal to the master station to start the diesel generator, and the diesel generator and the grid-forming energy storage operate together to meet the net load power.

[0093] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0094] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the above. More specific examples (a non-exhaustive list) of computer-readable storage media include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the above. The computer-readable storage medium used herein is not to be interpreted as a transient signal itself, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0095] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0096] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer, partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect through the Internet). In some embodiments, by using the state information of the computer-readable program instructions to personalize an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit may execute the computer-readable program instructions, thereby implementing various aspects of the present disclosure.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A coordinated control method for off-grid operation of a system with grid-connected energy storage, taking the difference between load power and the output power of a wind turbine generator set and the output power of a photovoltaic generator set as the net load power; characterized in that: include: Obtain the real-time state of charge, charge and discharge rate, and charge and discharge ratio of the grid-type energy storage, and obtain the maximum output power and minimum output power of the diesel generator set; Based on the output power change curve of the diesel generator set during the startup phase, determine the startup time required for the diesel generator set to reach the output power command value after it is started; based on the output power change curve of the diesel generator set during the shutdown phase, determine the shutdown time required for the diesel generator set to reach zero output power after it is shut down; The state of charge threshold for starting the diesel generator and the state of charge threshold for shutting down the diesel generator are determined by the following relationship: ， In the formula, is the charge state threshold for starting the diesel generator, is the charge state threshold for shutting down the diesel generator, and are the upper and lower limits of the state of charge of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, It is the start-up time required for the diesel generator set to reach the output power command value after it is turned on. It is the shutdown time required for the diesel generator set to output zero power after shutdown. is the state of charge margin value based on control delay and signal transmission delay; Real-time monitoring of the charge state of grid-connected energy storage; When the net load power is greater than zero and When the grid-connected energy storage sends a signal to the master station to start the diesel generator, the master station obtains the status signal of the diesel generator grid-connected circuit breaker and generates the diesel generator start-up command and output power command value; when When the grid-connected energy storage sends a signal to the master station to shut down the diesel generator, the master station obtains the status signal of the diesel generator grid-connected circuit breaker and generates a shutdown command for the diesel generator; When the net load power is greater than zero and When the discharge power of the grid-forming energy storage in the discharging state is greater than the net load power, the grid-forming energy storage discharges to meet the net load power; if the discharge power of the grid-forming energy storage in the discharging state is not greater than the net load power, the grid-forming energy storage sends a signal to the master station to start the diesel generator, and the diesel generator and the grid-forming energy storage operate together to meet the net load power.

2. The off-grid operation coordinated control method of a system containing grid-connected energy storage according to claim 1, characterized in that: By using the rated parameters of the grid-connected energy storage and the diesel generator, the state of charge threshold for starting the diesel generator and the state of charge threshold for shutting down the diesel generator corresponding to the start time of the off-grid operation coordinated control of the system are determined.

3. The off-grid operation coordinated control method of a system containing grid-connected energy storage according to claim 2, characterized in that: When the net load power is greater than zero and When the diesel generator is started, If the net load power is less than the minimum output power of the diesel generator, the minimum output power of the diesel generator is used as the output power command value of the diesel generator, and the grid-type energy storage is charged with the difference between the minimum output power of the diesel generator and the net load power; If the net load power is not less than the minimum output power of the diesel generator and less than the maximum output power of the diesel generator, the net load power is used as the output power command value of the diesel generator; when load disturbance or wind and solar power output fluctuation occurs in the system, the power shortage or surplus in the system is supplemented or absorbed by the grid-connected energy storage; If the net load power is greater than the maximum output power of the diesel generator, the maximum output power of the diesel generator will be used as the output power command value of the diesel generator, and the grid-type energy storage will be discharged to meet the shortfall of the net load power; if the grid-type energy storage discharge power cannot meet the shortfall of the net load power, the loads will be cut off in order from low to high in terms of their importance.

4. The off-grid operation coordinated control method of a system containing grid-connected energy storage according to claim 3 is characterized in that: When the net load power is less than zero and When the grid-connected energy storage is charged, it is charged with the absolute value of the net load power.

5. The off-grid operation coordinated control method of a system containing grid-connected energy storage according to claim 2, characterized in that: After shutting down the diesel generator, if the net load power is greater than zero, the grid-type energy storage discharges to meet the net load power. If the discharge power of the grid-type energy storage cannot meet the shortfall of the net load power, the loads are cut off in order of importance from low to high. After shutting down the diesel generator, if the net load power is less than zero, when the absolute value of the net load power is greater than the maximum charging power of the grid-type energy storage, the grid-type energy storage is charged with the absolute value of the net load power. If the absolute value of the net load power is not greater than the maximum charging power of the grid-type energy storage, the grid-type energy storage is charged with the maximum charging power.

6. The off-grid operation coordinated control method of a system containing grid-connected energy storage according to claim 2, characterized in that: Diesel generators and grid-connected energy storage operate together to meet the net load power, including: Start the diesel generator, and the output power command value of the diesel generator is the minimum output power; when the real-time charge state of the grid-type energy storage is less than Before and / or the running time of the diesel generator is not less than the operating limit, the master station adjusts the wind and solar output to meet the net load power shortage. If the net load power shortage cannot be met after adjusting the wind and solar output, the loads are cut in order from low to high in importance.

7. The off-grid operation coordinated control method of a system containing grid-connected energy storage according to claim 6, characterized in that: When the net load power is less than zero and When the grid-connected energy storage is charged, it is charged with the absolute value of the net load power.

8. The off-grid operation coordinated control method of a system containing grid-connected energy storage according to claim 1, characterized in that: When the running time of the diesel generator is greater than the running limit, the diesel generator sends a shutdown request signal to the master station; if the net load power is greater than zero, the master station controls the grid-type energy storage to use the output power command value before the diesel generator stops operating as the discharge power command to meet the net load power; if the net load power is less than zero and , the grid-type energy storage is charged with the absolute value of the net load power; if the net load power is less than zero and , the grid-type energy storage stops charging, and the master station controls the abandonment of wind power first and then solar power.

9. The off-grid operation coordinated control method of a system containing grid-connected energy storage according to claim 1, characterized in that: The diesel generator includes: a speed governor, a diesel prime mover and a synchronous generator; The speed regulator corrects the speed of the diesel engine according to the difference between the grid angular frequency setting value and the actual value of the angular frequency to output the actual value of the control torque; According to the actual value of the angular frequency, the difference between the actual value of the control torque and the set value of the control torque is compensated to obtain the control torque; The synchronous generator outputs a power command value driven by the control torque; Among them, the control torque setting value satisfies the following relationship: ， In the formula, is the control torque setting value, is the output power command value of the diesel generator, is the rated speed of the diesel generator.

10. A coordinated control system for off-grid operation of a system with grid-connected energy storage, which uses the difference between the load power and the output power of the wind turbine generator set and the output power of the photovoltaic generator set as the net load power; characterized in that: include: The acquisition module is used to obtain the real-time state of charge, charge and discharge rate, and charge and discharge ratio of the grid-type energy storage, and obtain the maximum output power and minimum output power of the diesel generator set; The threshold setting module is used to determine the starting time required for the diesel generator set to reach the output power command value after it is turned on based on the output power change curve of the diesel generator set in the starting stage; determine the shutdown time required for the diesel generator set to output zero after it is shut down based on the output power change curve of the diesel generator set in the shutdown stage; and determine the charge state threshold for starting the diesel generator and the charge state threshold for shutting down the diesel generator respectively according to the following relationship: ， In the formula, is the charge state threshold for starting the diesel generator, is the charge state threshold for shutting down the diesel generator, and are the upper and lower limits of the state of charge of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, is the charge and discharge rate of the grid-type energy storage, It is the start-up time required for the diesel generator set to reach the output power command value after it is turned on. It is the shutdown time required for the diesel generator set to output zero power after shutdown. is the state of charge margin value based on control delay and signal transmission delay; The coordination control module is used to monitor the charging state of the grid-type energy storage in real time; when the net load power is greater than zero and When , the grid-type energy storage sends a signal to the master station to start the diesel generator. The master station obtains the status signal of the diesel generator grid-connected circuit breaker and generates the diesel generator start-up instruction and output power instruction value; when When the net load power is greater than zero and When the discharge power of the grid-forming energy storage in the discharging state is greater than the net load power, the grid-forming energy storage discharges to meet the net load power; if the discharge power of the grid-forming energy storage in the discharging state is not greater than the net load power, the grid-forming energy storage sends a signal to the master station to start the diesel generator, and the diesel generator and the grid-forming energy storage operate together to meet the net load power.

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