Micro-grid energy storage system current-limiting black start method and device

Abstract

The present application relates to a kind of micro-grid energy storage system current-limiting black start method and device.The method comprises: S1.closing energy storage system incoming line ac circuit breaker, using constant frequency constant voltage control to start energy storage system to make voltage reference value increase;S2.comparing the load current I in energy storage system with the limit value I of load current limit : when the comparison result is I>I limit , open current-limiting PI controller to limit current, enter S3;When the comparison result is I≤I limit , judge whether energy storage system is in current-limiting state, the result is yes, enter S4, the result is no, enter S5;S3.judge whether load current is less than the expected value I of load current ref , the result is no, then continue to limit current;The result is yes, then close current-limiting PI controller to stop limiting current, enter step S4;S4.start voltage recovery mechanism to restore voltage reference value to the value before limiting current;Step S5.voltage reference value is continuously increased;S6.repeat steps S2-S5, until energy storage system voltage reference value reaches set value, and black start is completed.

Description

Technical Field

[0001] This invention relates to the field of black start for microgrid energy storage systems, and specifically to a current-limiting black start method and apparatus for microgrid energy storage systems. Background Technology 1.1 Background Technology

[0003] With the development of distributed energy generation technology, microgrid control technology has also made significant progress. A microgrid can function as a controllable unit, achieving self-control and protection, and can effectively coordinate the relationship between distributed power sources and the main power grid, enabling rapid grid development.

[0004] Black start refers to a situation where the entire system shuts down due to a fault, resulting in a complete power outage (excluding isolated small power grids that may still be operating), and is in a completely "dark" state. Without relying on other networks, the system recovers by starting generators with self-starting capabilities, which in turn drive generators without self-starting capabilities, gradually expanding the scope of system recovery, and ultimately achieving the recovery of the entire system.

[0005] When a microgrid operates independently, the energy storage system, as the main power source, needs to possess black-start capability. Microgrids typically contain a large number of transient loads, which can experience overcurrents of up to 5-7 times the rated current during startup, leading to black-start failure. Existing technologies using energy storage systems as the main power source for microgrid self-operation present the following technical challenges:

[0006] The black start process requires the removal of some loads before the black start is completed, and then the loads are gradually put back into operation. This results in insufficient black start capacity of the energy storage system, which not only prolongs the black start time of the microgrid but also causes inconvenience to operation.

[0007] 1.2 Prior Art Related to the Invention

[0008] 1.2.1 Technical solution of prior art 1

[0009] Chinese patent CN112736974A, entitled "A Black Start Method for Isolated Photovoltaic-Storage Microgrid Considering Battery Capacity Limitations," describes a technical solution that uses a diesel generator as the black start power source and an energy storage system as the non-black start power source. Before black start, all loads in the microgrid are disconnected; the black start power source is activated to establish the voltage and frequency of the microgrid system; and then the loads are gradually added.

[0010] 1.2.2 Disadvantages of Existing Technology 1

[0011] This technology requires all loads to be disconnected before a black start, and then gradually put back on according to the load level after the no-load black start is completed, thus finally completing the microgrid black start. This scheme is a no-load black start, which requires switching loads to achieve the microgrid black start, increasing the operational complexity and time of the black start process. At the same time, it is necessary to classify the loads first, but the microgrid loads and load levels are not static, which also brings difficulties to the later operation and maintenance.

[0012] 1.3 Prior Art Related to the Invention

[0013] 1.3.1 Technical solution of prior art 2

[0014] Chinese patent CN109066799A, entitled "A Black Start System and Method for Microgrids with Photovoltaic and Energy Storage," provides a black start method that does not depend on the remaining battery power or the remaining fuel of the diesel generator. Before black start, solar energy is used to power the converter control board, battery management system control board, and energy storage inverter control board. Then, the DC circuit breaker is closed to perform black start. The advantage of this solution is that the system can achieve black start as long as there is a solar energy system and any battery configuration.

[0015] 1.3.2 Disadvantages of Existing Technology Two

[0016] This technical solution uses solar energy to power each control board and prepares for black start, but it does not mention how the DC inverter and energy storage system work, nor does it mention how to handle situations where there are many motor-type loads in the load. 1.4 Prior Art Related to This Invention III

[0017] 1.4.1 Technical solution of existing technology three

[0018] Chinese patent CN106356892A, entitled "Microgrid Black Start Method," describes a method that involves: obtaining the remaining capacity of the energy storage batteries of each micro-source to be started; generating a black start sequence for micro-sources whose remaining energy storage batteries have a capacity greater than a preset value, based on their remaining capacity; obtaining the number of micro-sources to be started in the black start sequence; determining whether the number of micro-sources to be started in the black start sequence is within a preset value range; if so, starting the micro-sources in the black start sequence sequentially according to the black start sequence; determining whether the micro-sources in the black start sequence have been started completely; and if so, connecting the renewable energy generation unit and the load. This microgrid black start method ensures that there is sufficient energy to meet the load connection requirements during the black start process, thus improving the efficiency of black start.

[0019] 1.4.2 Disadvantages of Existing Technology Three

[0020] The proposed solution requires the micro-sources to be started sequentially to meet the load requirements, but it does not mention whether to start under load, how to coordinate between the micro-sources, or the type of load. Therefore, the applicability of this solution is limited. Summary of the Invention

[0021] The purpose of this invention is to provide a current-limiting black start method and system for a microgrid energy storage system, which can improve the black start capability of the energy storage system under load, thereby increasing the success rate of microgrid black start and reducing the black start time of the microgrid.

[0022] To achieve the above objectives, the present invention is implemented through the following technical solution.

[0023] This invention proposes a current-limiting black-start method for a microgrid energy storage system, the method comprising:

[0024] Step S1. Close the incoming AC circuit breaker of the energy storage system and start the energy storage system using constant frequency and constant voltage control to increase the voltage reference value;

[0025] Step S2. Compare the load current I in the energy storage system with the limit value I of the load current. limit The comparison result is I>I limit When the current is limited, the current-limiting PI controller is activated to limit the current, and the process proceeds to step S3; the comparison result is I≤I limit When the energy storage system is in a current-limiting state, determine whether it is in a current-limiting state. If the result is yes, proceed to step S4; if the result is no, proceed to step S5.

[0026] Step S3. Determine whether the load current is less than the expected value I of the load current. ref If the judgment result is negative, continue current limiting; if the judgment result is positive, shut down the current limiting PI controller to stop current limiting and proceed to step S4.

[0027] Step S4. Activate the voltage recovery mechanism to restore the voltage reference value to the value before current limiting;

[0028] Step S5. Continue to increase the voltage reference value;

[0029] Step S6. Repeat steps S2-S5 until the energy storage system voltage reference value reaches the set value, and the black start is completed.

[0030] As an improvement to the above technical solution, the method further includes: step S0. Checking relevant parameters of the energy storage system to confirm that a black start is enabled for the energy storage system; specifically including:

[0031] Step S0-1. Check the status of the PCC point switch and determine whether it is in the off state. If the result is no, continue to check and determine; if the result is yes, proceed to step S0-2.

[0032] Step S0-2. Determine whether the three-phase AC voltage is lower than M times the rated voltage, where M is 0.04 to 0.06; if the result is no, return to step S0-1; if the result is yes, enable black start and proceed to step S1.

[0033] As an improvement to the above technical solution, the constant frequency and constant voltage control in step S1 includes: starting the AC voltage using a zero-voltage soft start method, and using independent PI control for the amplitude of the three-phase AC voltage.

[0034] As one improvement to the above technical solution, the method of starting the AC voltage using a zero-voltage soft-start method specifically includes: controlling the AC voltage reference value to start from 0 and gradually increasing it according to a set rate of change until it reaches the set value U. exp until.

[0035] As one improvement to the above technical solution, the adjustment of the amplitude of the three-phase AC voltage using independent PI controllers specifically includes:

[0036] The line voltage of the AC power supply in the energy storage system is collected and converted to obtain the amplitude of the three-phase AC voltage.

[0037] The difference between the AC voltage amplitude of each phase and its respective desired voltage amplitude is calculated and input into the respective PI controller to obtain the voltage difference value that needs to be adjusted.

[0038] The adjusted three-phase AC voltage amplitude is obtained by summing the voltage difference that needs to be adjusted with the respective desired voltage amplitude.

[0039] As an improvement to the above technical solution, step S2 involves enabling the current-limiting PI controller for current limiting, specifically including:

[0040] The expected value of the load current I ref The difference between I and the load current I ek Input the current-limiting PI controller to obtain the voltage reduction value ΔU required for the energy storage system voltage reference value. out ;

[0041] Subtract ΔU from the voltage reference value out The new voltage reference value is used to reduce the load current for current limiting, while the voltage reference value before current limiting is recorded.

[0042] As one of the improvements to the above technical solution, the expected value of the load current I ref It is the load current limit value I limit k times, where 0 <k<1。

[0043] As one of the improvements to the above technical solution, the voltage recovery mechanism uses a linear recovery method to gradually reduce the output of the current-limiting PI controller to 0, so that the voltage reference value is restored to the value before current limiting.

[0044] This invention also proposes a current-limiting black-start device for a microgrid energy storage system, the device comprising:

[0045] The constant frequency and constant voltage control module is used to start the energy storage system using constant frequency and constant voltage control.

[0046] The load current acquisition and comparison module is used to compare the load current I in the energy storage system with the limit value I of the load current after the energy storage system is started. limit and expected value I ref Size;

[0047] A current limiting module is used when the load current I exceeds a limit value I. limit When the load current I is less than the expected value Iload current, the current-limiting PI controller is activated to limit the current, and the current is limited when the load current I is less than the expected value Iload current. ref When the current-limiting PI controller is turned off, current limiting stops; and

[0048] The voltage recovery module is used to restore the load current I when the load current I does not exceed the load current limit value I after the current limiting is enabled. limit When this happens, the voltage recovery mechanism is activated to restore the voltage reference value to its value before current limiting.

[0049] As an improvement to the above technical solution, the device also includes a status recognition module for checking relevant parameters of the energy storage system and confirming that a black start is initiated for the energy storage system.

[0050] The advantages of this invention compared to the prior art are:

[0051] 1) This invention provides a current-limiting black-start method for microgrid energy storage systems, overcoming the problem of insufficient black-start capability of energy storage systems with motor-type loads;

[0052] 2) This invention adjusts the output voltage according to the magnitude of the load current during the black start process, so that the instantaneous current during the start-up process is within the acceptable range of the energy storage system, thereby protecting the energy storage converter, improving the success rate of system black start, and shortening the black start time.

[0053] 3) After the current limiting measures are completed, the present invention adopts a gradual voltage recovery method, which reduces the load current change rate, reduces the impact and failure rate on the energy storage system, and improves the availability of the energy storage system. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the microgrid system composition of the present invention;

[0055] Figure 2 This is a schematic diagram of the control flow of the present invention;

[0056] Figure 3 Flowchart for status recognition startup;

[0057] Figure 4 A schematic diagram showing the AC voltage reference value for soft-start AC voltage;

[0058] Figure 5 This is a schematic diagram of AC voltage control.

[0059] Figure 6 This is a schematic diagram of the voltage recovery curve. Detailed Implementation

[0060] The technical solutions provided by the present invention will be further illustrated below with reference to the embodiments.

[0061] like Figure 1 The diagram shown is a schematic representation of a microgrid system as described in this invention. The microgrid system includes: an energy storage converter, a battery, photovoltaic power, wind power, and loads, as shown below. Figure 1 Energy storage components are connected to the corresponding energy storage converter; the energy storage converter, solar power generation, wind power generation, and load AC side are connected to the AC bus, and the power grid is powered by the diesel generator; when the diesel generator malfunctions or needs to be converted to pure green energy, the energy storage converter provides a stable AC power supply.

[0062] Example 1

[0063] like Figure 2 As shown, the current-limiting black-start control block diagram of the present invention is as follows. It mainly includes modules such as constant frequency and constant voltage control, current-limiting measures, and voltage recovery; the current-limiting black-start method for a microgrid energy storage system of the present invention specifically includes the following steps:

[0064] 1. Constant frequency and constant voltage control

[0065] (1) Status Identification: The energy storage converter detects the status of the PCC (Point of Common Coupling) switch and the three-phase AC voltage. If the PCC switch is open and the three-phase AC voltage is lower than 0.05 times the rated voltage, proceed to the next step; if... Figure 3 The diagram shown is a flowchart of the state recognition process.

[0066] (2) Start constant frequency and constant voltage control: Close the incoming AC circuit breaker of the energy storage system. After the circuit breaker is closed, start constant frequency and constant voltage control.

[0067] (3) Constant frequency and constant voltage control: Zero-voltage soft start mode is adopted and the three-phase voltage is controlled independently by PI.

[0068] AC voltage reference value changes are adopted Figure 4 The method described above involves setting the AC voltage reference to 0 and gradually increasing it according to a set rate of change until the desired voltage U is reached. exp until.

[0069] AC voltage closed-loop control such as Figure 5 The three-phase AC voltage amplitude is controlled independently by PI, with a phase angle difference of 120°.

[0070] 2. Traffic control measures

[0071] (1) Set the load current limit value I limit This value is set to 1.1 times the rated AC current of the energy storage converter;

[0072] (2) Using the load current limit value I limit k times the expected value of the load current I ref , of which 0 <k<1;

[0073] (3) Using the expected value of the load current I ref The difference between I and the load current I ek As the input to the PI controller, the portion ΔU that needs to be reduced from the energy storage system voltage reference value is... out As the output of a current-limiting PI controller;

[0074] (4) Utilizing the load current limit value I limit The relationship between the load current I and the current-limiting PI controller controls the opening and closing of the current-limiting controller.

[0075] When the load current I is greater than the load current limit I limit Immediately activate the current-limiting PI controller;

[0076] When the load current I is less than the expected value of the load current I ref At this time, the input of the current-limiting PI controller is cleared to zero.

[0077] 3 Voltage Recovery

[0078] The voltage recovery step refers to gradually reducing the output of the current-limiting PI controller to 0, restoring the voltage reference value to its value before current limiting; a linear recovery method is used, and the curve is as follows. Figure 6 As shown.

[0079] When the load current I is less than the expected value of the load current I ref At that time, the flow restriction measures will be lifted;

[0080] When the load current I is not greater than the load current limit I limit At that time, the voltage recovery mechanism is activated.

[0081] 4. Boost Control

[0082] After the voltage reference value is restored to the value before current limiting, repeat steps 2.2.1 to 2.2.3 until the system voltage reaches the set value and black start is completed.

[0083] Example 2

[0084] The present invention provides a current-limiting black-start device for a microgrid energy storage system, comprising: a constant frequency and constant voltage control module, a load current acquisition and comparison module, a current-limiting module, and a voltage recovery module;

[0085] The constant frequency and constant voltage control module is used to start the energy storage system using constant frequency and constant voltage control.

[0086] The load current acquisition and comparison module is used to compare the load current I in the energy storage system with the limit value I of the load current after the energy storage system is started. limit and expected value I ref Size;

[0087] A current limiting module is used when the load current I exceeds a limit value I. limit When the load current I is less than the expected value Iload current, the current-limiting PI controller is activated to limit the current, and the current is limited when the load current I is less than the expected value Iload current. ref When the current limiting PI controller is turned off, current limiting is stopped.

[0088] The voltage recovery module is used to restore the load current I when the load current I does not exceed the load current limit value I after the current limiting is enabled. limit When this happens, the voltage recovery mechanism is activated to restore the voltage reference value to its value before current limiting.

[0089] The microgrid energy storage system current limiting black start device of the present invention further includes a status identification module; the status identification module is used to check the relevant parameters of the energy storage system and confirm that the black start of the energy storage system is enabled.

[0090] As can be seen from the above detailed description of the present invention, the present invention adjusts the output voltage according to the magnitude of the load current during the black start process, so that the instantaneous current during the start process is within the acceptable range of the energy storage system, thereby protecting the energy storage converter, improving the success rate of system black start, and shortening the black start time.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A current-limiting black-start method for a microgrid energy storage system, the method comprising: Step S1. Close the incoming AC circuit breaker of the energy storage system and start the energy storage system using constant frequency and constant voltage control to increase the voltage reference value; Step S2. Compare the load current I in the energy storage system with the limit value I of the load current. limit The comparison result is I>I limit When the current is limited, the current-limiting PI controller is activated to limit the current, and the process proceeds to step S3; the comparison result is I≤I limit When the current is limited, determine whether the energy storage system is in a current-limiting state. If the result is yes, turn off the current-limiting PI controller to stop current limiting and proceed to step S4. If the result is no, proceed to step S5. Step S3. Determine whether the load current is less than the expected value I of the load current. ref If the judgment result is negative, then traffic restriction will continue. If the judgment result is yes, then the current limiting PI controller is turned off to stop current limiting, and the process proceeds to step S4; Step S4. Activate the voltage recovery mechanism to restore the voltage reference value to the value before current limiting; Step S5. Continue to increase the voltage reference value; Step S6. Repeat steps S2-S5 until the energy storage system voltage reference value reaches the set value, and the black start is completed; Specifically, step S2, which involves enabling the current-limiting PI controller for current limiting, includes: The expected value of the load current I ref The difference between I and the load current I ek Input the current-limiting PI controller to obtain the voltage reduction value ΔU required for the energy storage system voltage reference value. out ; Subtract ΔU from the voltage reference value out The new voltage reference value is used to reduce the load current for current limiting, while the voltage reference value before current limiting is recorded.

2. The current-limiting black-start method for a microgrid energy storage system according to claim 1, characterized in that, The method further includes: step S0. Checking relevant parameters of the energy storage system to confirm that a black start is enabled for the energy storage system; specifically including: Step S0-1. Check the status of the PCC point switch and determine whether it is in the off state. If the result is no, continue to check and determine; if the result is yes, proceed to step S0-2. Step S0-2. Determine whether the three-phase AC voltage is lower than M times the rated voltage, where M is 0.04~0.06; if the result is no, return to step S0-1; if the result is yes, enable black start and proceed to step S1.

3. The current-limiting black-start method for a microgrid energy storage system according to claim 1, characterized in that, The constant frequency and constant voltage control in step S1 includes: starting the AC voltage using a zero-voltage soft start method, and using independent PI control for the amplitude of each of the three-phase AC voltages.

4. The current-limiting black-start method for a microgrid energy storage system according to claim 3, characterized in that, The method of starting the AC voltage using zero-voltage soft start specifically includes: controlling the AC voltage reference value to start from 0 and gradually increasing it according to a set rate of change until it reaches the set value U. exp until.

5. The current-limiting black-start method for a microgrid energy storage system according to claim 3, characterized in that, The adjustment of the amplitude of the three-phase AC voltage using independent PI controllers specifically includes: The line voltage of the AC power supply in the energy storage system is collected and converted to obtain the amplitude of the three-phase AC voltage. The difference between the AC voltage amplitude of each phase and its respective desired voltage amplitude is calculated and input into the respective PI controller to obtain the voltage difference value that needs to be adjusted. The adjusted three-phase AC voltage amplitude is obtained by summing the voltage difference that needs to be adjusted with the respective desired voltage amplitude.

6. The current-limiting black-start method for a microgrid energy storage system according to claim 1, characterized in that, The expected value I of the load current ref It is the limit value I of the load current. limit k times, where 0 <k<1。 7. The current-limiting black-start method for a microgrid energy storage system according to claim 1, characterized in that, The voltage recovery mechanism uses a linear recovery method to gradually reduce the output of the current-limiting PI controller to 0, so that the voltage reference value is restored to the value before current limiting.

8. A current-limiting black-start device for a microgrid energy storage system, characterized in that, The device includes: The constant frequency and constant voltage control module is used to start the energy storage system using constant frequency and constant voltage control. The load current acquisition and comparison module is used to compare the load current I in the energy storage system with the limit value I of the load current after the energy storage system is started. limit and expected value I ref Size; A current limiting module is used when the load current I exceeds a limit value I. limit When the load current I is less than the expected value Iload current, the current-limiting PI controller is activated to limit the current, and the current is limited when the load current I is less than the expected value Iload current. ref When the current limiting PI controller is turned off to stop current limiting, the step of turning on the current limiting PI controller to perform current limiting specifically includes: setting the expected value I of the load current. ref The difference between I and the load current I ek Input the current-limiting PI controller to obtain the voltage reduction value ΔU required for the energy storage system voltage reference value. out Subtract ΔU from the voltage reference value out As a new voltage reference value, current limiting is implemented to reduce load current, while the voltage reference value before current limiting is recorded; and The voltage recovery module is used to restore the load current I when the load current I does not exceed the load current limit value I after the current limiting is enabled. limit When this happens, the voltage recovery mechanism is activated to restore the voltage reference value to its value before current limiting.

9. The microgrid energy storage system current-limiting black-start device according to claim 8, characterized in that, The device also includes a status recognition module for checking relevant parameters of the energy storage system and confirming that a black start has been initiated for the energy storage system.

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