Island detection method of energy storage hydrogen production system, medium and detection system

Abstract

The invention discloses an island detection method of an energy storage hydrogen production system, a medium and a system, and the detection method comprises the steps: 1) obtaining the voltage of the energy storage hydrogen production system, carrying out the phase locking to generate an angle theta grid, obtaining the voltage of an output port of a converter, carrying out the phase locking to generate an angle theta pcs, and comparing the angle theta grid with the angle theta pcs to obtain a difference value delta theta; 2) comparing the difference value delta theta with a preset threshold value; and when the difference value delta theta is greater than a preset threshold value, judging that the energy storage hydrogen production system is in an island state, and actively performing island protection. According to the invention, active / passive anti-islanding protection is defined according to the difference value between the phase-locking angle of the grid-connected point and the phase-locking angle of the converter port, and the frequency deviation is detected through active disturbance and sliding window filtering so as to detect the islanding, so that the detection blind area of passive anti-islanding is reduced, and the response speed is improved.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of converters, and in particular to an island detection method, a medium and a detection system for an energy storage hydrogen production system. Background Art

[0002] Grid-connected constant power operation and off-grid operation are the two main functions of energy storage converters. In the grid-connected constant power operation mode, PCS can charge and discharge, and PCS performs stable charging / discharging according to dispatch instructions. Usually, when the load of the power grid is at a low point, PCS charges the battery in constant power mode and stores the remaining electric energy at this time. When the load of the power grid is at a peak point, PCS discharges the battery in constant power mode. Thus, PCS can adjust the peak and valley load of the power grid on the load side, playing the role of peak shaving and valley filling. The existence of energy storage and its converter can not only reduce the installed capacity in the power system, but also significantly reduce the line impedance, supply power nearby, improve the utilization rate of power transmission and distribution equipment, and save energy and reduce costs.

[0003] When the PCS is working in an off-grid state, the converter establishes an AC voltage with stable amplitude and frequency on the grid side and performs voltage-frequency control. This control mode is particularly suitable for scenarios such as remote areas, islands, and distributed microgrids, providing voltage source support for AC loads, or providing starting power for power generation equipment applications with "black start" function requirements.

[0004] When the energy storage power station works in the discharge mode, the local load it carries is powered by the power grid and PCS at the same time. When the power grid is disconnected, the local load of the energy storage system forms an isolated power system, which is called the "island" phenomenon. Islands can be divided into two types: planned islands and unplanned islands. Among them, planned islands refer to maintaining the operation of the island system in a stable and reliable state. The control system pre-calibrates a reasonable island area based on the capacity of the energy storage and the local load power. When the power grid is disconnected, it can enter the island state without major adjustment actions, and keep the voltage in the island stable and the power supply reasonable.

[0005] Unplanned islanding refers to a situation where, due to a fault on the grid side, the grid-connected switch trips, and the energy storage device continues to supply power to the surrounding local loads, forming an island state that the power system cannot control. When the load is separated from the grid, the power between the energy storage device and the local load is unbalanced. Long-term operation will cause abnormal load supply voltage and frequency, which will damage the energy storage system and local electrical equipment. At the same time, because the wires and load equipment in the island system are still energized, it is easy to cause electric shock hazards to personnel during maintenance, and affect the automatic devices, protection actions and reclosing in the system. In view of the large number of hazards of unplanned islanding, energy storage equipment needs to be equipped with anti-islanding protection function, so that the energy storage converter can quickly detect and disconnect from the grid when it is working with unplanned islanding.

[0006] At present, relevant standards have been formulated at home and abroad to put forward specific requirements for the anti-islanding capability of energy storage inverters. GBT34120-2017 "Technical Specifications for Energy Storage Inverters of Electrochemical Energy Storage Systems" stipulates that if the frequency deviation value of the energy storage inverter exceeds the ±0.5Hz range after the grid-connected energy storage inverter, the over / under-frequency protection should be activated within 0.2s, and the energy storage inverter should be disconnected from the grid. When the grid is lost, the anti-islanding protection should be activated within 2s to disconnect the energy storage system from the grid. Similarly, NBT 31016-2019 "Technical Specifications for Battery Energy Storage Power Control System Inverters" also requires that when the power supply of the grid to which the energy storage inverter is connected is interrupted, the inverter should stop supplying power to the grid within 2s and send an islanding protection warning signal. Summary of the invention

[0007] The technical problem to be solved by the present invention is: in view of the technical problems existing in the prior art, the present invention provides an islanding detection method, medium and detection system for an energy storage hydrogen production system that clearly defines active and passive anti-islanding protection.

[0008] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0009] A method for detecting an island in an energy storage hydrogen production system comprises the following steps:

[0010] 1) Obtain the voltage of the energy storage hydrogen production system and perform phase locking to generate the angle θ _grid , obtain the voltage at the output port of the converter and perform phase locking to generate the angle θ _pcs , the angle θ _grid With angle θ _pcs Compare and get the difference Δθ=θ _grid -θ _pcs ;

[0011] 2) Compare the difference Δθ with a preset threshold; when the difference Δθ is greater than the preset threshold, the energy storage hydrogen production system is judged to be in an island state, and island protection is actively performed.

[0012] Preferably, in step 2), when the difference Δθ is not greater than a preset threshold, the following steps are performed:

[0013] 3) Fixedly injecting an initial disturbance into a power control link of the energy storage hydrogen production system, wherein the initial disturbance includes a first active power and a first reactive power;

[0014] 4) The frequency deviation is detected by sliding window filtering to obtain the sliding window frequency deviation;

[0015] 5) Compare the sliding window frequency deviation with a first preset value; when the sliding window frequency deviation is greater than the first preset value, it is determined that the energy storage hydrogen production system is in an island state, and passive island protection is performed.

[0016] Preferably, in step 5), when the sliding window frequency deviation is less than the second preset value and greater than the third preset value, the process proceeds to step:

[0017] 6) Fixedly injecting a correction disturbance into the power control link, and simultaneously adding a phase angle deviation feedforward disturbance to the phase-locked angle; wherein the correction disturbance comprises a second active power and a second reactive power, wherein the frequency of the second active power is less than the frequency of the first active power, and the frequency of the second reactive power is less than the frequency of the first reactive power;

[0018] 7) The frequency deviation is detected by sliding window filtering to obtain the sliding window frequency deviation;

[0019] 8) Compare the sliding window frequency deviation with a fourth preset value; when the sliding window frequency deviation is greater than the fourth preset value, the energy storage hydrogen production system is judged to be in an island state, and passive island protection is performed; wherein the first preset value>the second preset value>the fourth preset value>the third preset value.

[0020] Preferably, in step 8), when the sliding window frequency deviation is not greater than a fourth preset value, the process returns to step 3) and cancels the phase angle deviation feedforward disturbance.

[0021] Preferably, the detection formula of sliding window filtering is:

[0022]

[0023]

[0024] Δf=f-f0

[0025] Where Δf is the difference between the frequency f detected by the phase-locked loop in real time and the basic frequency f0, and N is the sliding window time width M sw The program execution cycle T s The quotient of represents the number of sliding window calculation points; Δf sw is the frequency deviation after sliding window filtering.

[0026] Preferably, the first active power and the first reactive power corresponding to the initial disturbance amount are respectively:

[0027]

[0028] Preferably, the second active power and the second reactive power corresponding to the corrected disturbance amount are respectively:

[0029]

[0030] Preferably, when entering the island protection mode, the pulses of the energy storage converter are blocked and the energy storage converter is disconnected from the power grid.

[0031] The present invention also discloses a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method described above are executed.

[0032] The present invention further discloses an island detection system for an energy storage hydrogen production system, comprising:

[0033] The first program module is used to obtain the voltage of the energy storage hydrogen production system and perform phase locking to generate the angle θ _grid , obtain the voltage at the output port of the converter and perform phase locking to generate the angle θ _pcs , the angle θ _grid With angle θ _pcs Compare and get the difference Δθ=θ _grid -θ _pcs ;

[0034] The second program module is used to compare the difference Δθ with a preset threshold; when the difference Δθ is greater than the preset threshold, it is determined that the energy storage hydrogen production system is in an island state and island protection is actively performed.

[0035] Compared with the prior art, the advantages of the present invention are:

[0036] The active / passive combined islanding detection and protection method proposed in the present invention defines active / passive anti-islanding protection by judging the difference between the voltage phase of the grid connection point and the voltage phase of the converter output terminal, thereby preventing excessive power disturbance from being injected during the active anti-islanding protection process and enabling faster response during the active protection process.

[0037] In working conditions where "detection blind spots" are prone to occur, such as "perfect resonance" and excessive local resistance or capacitance load, the present invention actively disturbs the active and reactive amplitudes (low-frequency harmonics) and phases, and then detects the frequency deviation through sliding window filtering. The island is detected based on the sliding window frequency deviation, which greatly reduces the "detection blind spot" of the passive anti-islanding protection. At the same time, it can perform rapid protection actions within the specified time according to the standard gradient, thereby improving the protection response speed.

[0038] The present invention uses the sliding window frequency deviation as an islanding criterion, superimposes disturbances layer by layer, and actively reduces disturbances when the islanding state cannot be detected, thereby greatly reducing the detection blind area and being able to quickly detect the islanding state. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a topological structure diagram of the energy storage and hydrogen production system in an embodiment of the present invention.

[0040] Figure 2 The flowchart of the island detection method in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0042] like Figure 2 As shown, the island detection method of the energy storage hydrogen production system according to the embodiment of the present invention comprises the steps of:

[0043] 1) Obtain the voltage of the energy storage hydrogen production system and perform phase locking to generate the angle θ _grid , obtain the voltage at the output port of the converter and perform phase locking to generate the angle θ _pcs , the angle θ _grid With angle θ _pcs Compare and get the difference Δθ=θ _grid -θ _pcs ;

[0044] 2) Compare the difference Δθ with a preset threshold; when the difference Δθ is greater than the preset threshold, the energy storage hydrogen production system is judged to be in an island state, and active island protection is performed; when the difference Δθ is not greater than the preset threshold, enter step 3) to perform passive anti-islanding detection;

[0045] 3) Fixedly injecting an initial disturbance into the power control link of the energy storage hydrogen production system; the initial disturbance is the first active power and the first reactive power of 0.001 pu at a frequency of 35 Hz;

[0046] 4) The frequency deviation is detected by sliding window filtering to obtain the sliding window frequency deviation;

[0047] 5) Compare the sliding window frequency deviation with a first preset value (such as 0.3 Hz); when the sliding window frequency deviation is greater than the first preset value, the energy storage hydrogen production system is judged to be in an island state, and passive island protection is performed; when the sliding window frequency deviation is less than the second preset value (0.25 Hz) and greater than the third preset value (0.2 Hz), proceed to step 6); wherein the first preset value> the second preset value> the third preset value;

[0048] 6) Fixedly injecting a correction disturbance into the power control link, and simultaneously adding a phase angle deviation feedforward disturbance to the phase-locked angle; wherein the correction disturbance comprises a second active power and a second reactive power of 0.25 Hz and 0.001 pu, wherein the frequency of the second active power is less than the frequency of the first active power, and the frequency of the second reactive power is less than the frequency of the first reactive power;

[0049] 7) The frequency deviation is detected by sliding window filtering to obtain the sliding window frequency deviation;

[0050] 8) Compare the sliding window frequency deviation with the fourth preset value (such as 0.234Hz); when the sliding window frequency deviation is greater than the fourth preset value, the energy storage hydrogen production system is judged to be in an island state and enters passive anti-island protection; wherein the first preset value> the second preset value> the fourth preset value> the third preset value; when the sliding window frequency deviation is not greater than the fourth preset value, return to step 3) and cancel the phase angle deviation feedforward disturbance to reduce the phenomenon of power quality deterioration caused by active disturbance.

[0051] The active / passive combined islanding detection and protection method of the present invention defines active / passive anti-islanding protection by judging the difference between the voltage phase of the grid connection point and the voltage phase of the inverter output terminal, thereby preventing excessive power disturbance from being injected during the active anti-islanding protection process and enabling faster response during the active protection process.

[0052] In working conditions where "detection blind spots" are prone to occur, such as "perfect resonance" and excessive local resistance or capacitance load, the present invention actively disturbs the active and reactive amplitudes (low-frequency harmonics) and phases, and then detects the frequency deviation through sliding window filtering. The island is detected based on the sliding window frequency deviation, which greatly reduces the "detection blind spot" of the passive anti-islanding protection. At the same time, it can perform rapid protection actions within the specified time according to the standard gradient, thereby improving the protection response speed.

[0053] The present invention uses the sliding window frequency deviation as an islanding criterion, superimposes disturbances layer by layer, and actively reduces disturbances when the islanding state cannot be detected, thereby greatly reducing the detection blind area and being able to quickly detect the islanding state.

[0054] The present invention also discloses a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method described above are executed.

[0055] The present invention further discloses an island detection system for an energy storage hydrogen production system, comprising:

[0056] The first program module is used to obtain the voltage of the energy storage hydrogen production system and perform phase locking to generate the angle θ _grid , obtain the voltage at the output port of the converter and perform phase locking to generate the angle θ _pcs , the angle θ _grid With angle θ _pcs Compare and get the difference Δ

[0057] θ=θ _grid -θ _pcs ;

[0058] The second program module is used to compare the difference Δθ with a preset threshold; when the difference Δθ is greater than the preset threshold, it is determined that the energy storage hydrogen production system is in an island state and island protection is actively performed.

[0059] The medium and system of the present invention correspond to the above detection method and also have the advantages described in the above detection method.

[0060] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods:

[0061] The "island system" formed by the three-level energy storage converter, local load and power grid is as follows: Figure 1 shown. Figure 1 In the process, the energy storage converter works in the discharge state, and the energy storage system provides energy to the outside.

[0062] Figure 1 P _grid , Q _grid Respectively represent the active power and reactive power provided by the power grid to the local load; P _pcs , Q _pcs Respectively represent the active and reactive power provided by the energy storage system to the local load; P _load , Q _load Respectively represent the active and reactive power flowing into the local load;

[0063] When the island state does not occur and the power grid maintains a stable working state, the following relationship exists:

[0064]

[0065] The angle generated by phase-locking the voltage collected at the common connection point of the power grid through the grid-connected switch cabinet is defined as θ_gr id, and the angle generated by phase-locking the voltage at the output port of the converter through the controller is defined as θ_pcs. In the steady-state operation of the power grid and the energy storage converter, the difference between θ_gr id and θ_pcs, Δθ = θ_gr id-θ_pcs, is a fixed value. When an island state occurs, the power grid is missing, and P_gr id and Q_gr id are equal to 0. At this time, if P_pcs, Q_pcs do not match P_load, Q_load (i.e. P_pcs≠P_load, Q_pcs≠Q_load), the voltage and frequency of the converter output port will change, and the difference Δθ between the grid-connected point phase-locking angle θ_grid and the converter port phase-locking angle θ_pcs will inevitably change. The range of change of Δθ is judged within a certain period of time; when it is greater than a certain threshold value (i.e. the preset threshold value, the range value is selected as 0.234*2pi), it is judged as an island state, that is, active island protection is performed.

[0066] When an island state occurs, and P _pcs , Q _pcs With P _load , Q_load Complete match (i.e. P _pcs =P _load , Q _pcs =Q _load ), that is, the "perfect resonance" state occurs. At this time, the voltage and frequency of the converter output port will not change, and the grid-connected point phase-locking angle θ _grid Phase lock angle θ with converter port _pcs The difference Δθ will not change significantly. At this time, passive anti-islanding detection is required.

[0067] In order to minimize the blind spot of anti-islanding detection under the "perfect resonance" state, active disturbances of active power, reactive power amplitude (low-frequency harmonics) and phase are adopted to carry out detection in a progressive manner.

[0068] Since the standard requires the detection of islanding when the frequency deviation exceeds ±0.5Hz, in order to prevent the existence of a detection blind spot in the "perfect resonance" state, the grid is cut off without any frequency change. At this time, first inject 35Hz, 0.001pu active and reactive power disturbances (corresponding to the initial disturbance amount) into the power control link, as follows:

[0069]

[0070] Due to the injection of the initial disturbance, frequency deviation will be caused in the island state. When the sliding window frequency deviation is detected to be greater than 0.3Hz (corresponding to the first preset value), the island protection can be directly triggered, the pulse is blocked, and the energy storage converter is disconnected from the grid. When it is detected that the sliding window frequency is still less than 0.25Hz (corresponding to the second preset value), but greater than 0.2Hz (corresponding to the third preset value), the active and reactive disturbance frequencies are changed to 25Hz as follows (corresponding to the corrected disturbance):

[0071]

[0072] At the same time, a positive feedforward disturbance of the difference Δθ between the grid-connected point phase-locking angle and the converter port phase-locking angle is added to the phase-locking angle. At this time, if it is detected that the sliding window frequency deviation is greater than 0.234 Hz ​​(corresponding to the fourth preset value), the anti-islanding protection can be triggered; if the sliding window frequency deviation is not greater than 0.234 Hz, the power disturbance returns to the basic disturbance of 35 Hz, and the phase-locking angle difference feedforward disturbance is canceled, thereby reducing the phenomenon of power quality deterioration caused by active disturbance.

[0073] In the above frequency deviation detection process, in order to prevent false operation, the frequency deviation is detected by sliding window filtering, and the detection method is as follows:

[0074]

[0075]

[0076] Δf=f-f0

[0077] In the above formula, Δf is the difference between the frequency f detected by the phase-locked loop in real time and the basic frequency f0 (taken as 50Hz), N is the quotient of the sliding window time width Msw and the program execution period Ts, which represents the number of sliding window calculation points, where the sliding window width is set to 25ms; Δfsw is the frequency deviation after sliding window filtering. By using the frequency deviation after sliding window filtering as the criterion for superimposed disturbance, it is possible to prevent false actions caused by sampling deviations (sliding window filtering is to superimpose the sampling values ​​of a certain period and then divide the value obtained by the number of periods. It is relatively stable compared to the directly sampled value, and can prevent false judgments and actions caused by sampling errors or external disturbances).

[0078] The above are only preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for detecting an island in an energy storage hydrogen production system, characterized in that: The following steps are involved: 1) Obtain the voltage of the energy storage hydrogen production system and perform phase locking to generate the angle θ _grid , obtain the voltage at the output port of the converter and perform phase locking to generate the angle θ _pcs , the angle θ _grid With angle θ _pcs Compare and get the difference Δθ=θ _grid -θ _pcs ; 2) Compare the difference Δθ with a preset threshold; when the difference Δθ is greater than the preset threshold, the energy storage hydrogen production system is judged to be in an island state, and island protection is actively performed.

2. The island detection method for the energy storage hydrogen production system according to claim 1, characterized in that: In step 2), when the difference Δθ is not greater than the preset threshold, the following steps are performed: 3) Fixedly injecting an initial disturbance into a power control link of the energy storage hydrogen production system, wherein the initial disturbance includes a first active power and a first reactive power; 4) The frequency deviation is detected by sliding window filtering to obtain the sliding window frequency deviation; 5) Compare the sliding window frequency deviation with a first preset value; when the sliding window frequency deviation is greater than the first preset value, it is determined that the energy storage hydrogen production system is in an island state, and passive island protection is performed.

3. The island detection method for the energy storage hydrogen production system according to claim 2 is characterized in that: In step 5), when the sliding window frequency deviation is less than the second preset value and greater than the third preset value, the following steps are performed: 6) Fixedly injecting a correction disturbance into the power control link, and simultaneously adding a phase angle deviation feedforward disturbance to the phase-locked angle; wherein the correction disturbance comprises a second active power and a second reactive power, wherein the frequency of the second active power is less than the frequency of the first active power, and the frequency of the second reactive power is less than the frequency of the first reactive power; 7) The frequency deviation is detected by sliding window filtering to obtain the sliding window frequency deviation; 8) Compare the sliding window frequency deviation with a fourth preset value; when the sliding window frequency deviation is greater than the fourth preset value, the energy storage hydrogen production system is judged to be in an island state, and passive island protection is performed; wherein the first preset value>the second preset value>the fourth preset value>the third preset value.

4. The island detection method for the energy storage hydrogen production system according to claim 3 is characterized in that: In step 8), when the sliding window frequency deviation is not greater than the fourth preset value, return to step 3) and cancel the phase angle deviation feedforward disturbance.

5. The island detection method for the energy storage hydrogen production system according to claim 2, 3 or 4, characterized in that: The detection formula of sliding window filtering is: Δf=f-f0 Where Δf is the difference between the frequency f detected by the phase-locked loop in real time and the basic frequency f0, and N is the sliding window time width M sw The program execution cycle T s The quotient of represents the number of sliding window calculation points; Δf sw is the frequency deviation after sliding window filtering.

6. The island detection method for the energy storage hydrogen production system according to claim 3 or 4, characterized in that: The first active power and the first reactive power corresponding to the initial disturbance are:

7. The island detection method for the energy storage hydrogen production system according to claim 6, characterized in that: The second active power and the second reactive power corresponding to the corrected disturbance are respectively:

8. The island detection method for the energy storage hydrogen production system according to claim 1, 2, 3 or 4, characterized in that: When entering the island protection mode, the pulse of the energy storage converter is blocked and the energy storage converter is disconnected from the power grid.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: The computer program executes the steps of the method according to any one of claims 1 to 8 when executed by a processor.

10. An island detection system for an energy storage hydrogen production system, characterized in that: include: The first program module is used to obtain the voltage of the energy storage hydrogen production system and perform phase locking to generate the angle θ _grid , obtain the voltage at the output port of the converter and perform phase locking to generate the angle θ _pcs , the angle θ _grid With angle θ _pcs Compare and get the difference Δθ=θ _grid -θ _pcs ; The second program module is used to compare the difference Δθ with a preset threshold; when the difference Δθ is greater than the preset threshold, it is determined that the energy storage hydrogen production system is in an island state and island protection is actively performed.

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