A method and system for detecting islanding of a high-voltage chain energy storage system

Abstract

An island detection method and system based on a high-voltage chain energy storage system includes the following steps: by phase-locking the phase-locked loop of the three-phase AC voltage of the high-voltage chain energy storage system, a voltage phase angle Angle is obtained; according to the voltage phase angle Angle and the control period T of the energy storage control system, a first Angle and a second Angle are obtained, wherein the first Angle and the second Angle are values ​​of two adjacent control periods; according to the first Angle and the second Angle, a grid voltage frequency Freq_Cal is calculated; if the absolute value of the difference between Freq_Cal and the reference frequency Freq_Ref exceeds the island check frequency difference threshold value DeltFreq, it is determined that an island phenomenon occurs in the energy storage system. The present invention can realize rapid detection of AC grid faults, prevent the energy storage system from operating in an island state, ensure that the protection device of the grid system can operate correctly, and make the grid operate within the control range of the power company.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic control, and more specifically, relates to an island detection method and system for a high-voltage chain energy storage system. Background Art

[0002] The islanding phenomenon refers to the situation where, due to a grid system failure or power outage for maintenance, the grid-connected power generation or energy storage system fails to detect the power outage in time and cannot quickly disconnect itself from the grid system, resulting in a self-sufficient power supply island phenomenon that the power company cannot control and where the grid-connected power generation or energy storage system supplies power to the surrounding loads off-grid.

[0003] Islanding operation not only causes damage to the entire power grid equipment, but may even threaten the personal safety of maintenance personnel. Therefore, it is particularly important to install an anti-islanding protection device in the grid-connected power generation or energy storage system to detect the arc island effect and disconnect the grid-connected power generation or energy storage system from the power grid in time. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the purpose of the present invention is to provide a control device for a high-voltage chain energy storage system, implement a method for detecting island operation of the high-voltage chain energy storage system, and ensure the safety of the power grid. Further, a method for detecting island operation of a high-voltage chain energy storage system is proposed.

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

[0006] An island detection method based on a high-voltage chain energy storage system comprises the following steps:

[0007] Step 1, by phase-locking the phase-locked loop of the three-phase AC voltage of the high-voltage chain energy storage system, the voltage phase angle Angle is obtained;

[0008] Step 2, obtaining a first Angle and a second Angle according to the voltage phase angle Angle and the control period T of the energy storage control system, wherein the first Angle and the second Angle are values ​​of two adjacent control periods;

[0009] Step 3, calculating the grid voltage frequency Freq_Cal according to the first Angle and the second Angle;

[0010] Step 4: If the absolute value of the difference between Freq_Cal and the reference frequency Freq_Ref exceeds the islanding check frequency difference threshold value DeltFreq, it is determined that an islanding phenomenon occurs in the energy storage system.

[0011] Furthermore, step 1 specifically includes:

[0012] Step 11, performing phase locking through a phase-locked loop of a three-phase AC voltage and performing abc / dq coordinate transformation;

[0013] Step 12, extracting the positive sequence voltage;

[0014] Step 13, taking the positive sequence voltage as the input of the PI regulation link, and outputting it as the voltage phase angle.

[0015] Furthermore, in step 11:

[0016] The abc / dq coordinate transformation is:

[0017]

[0018] Where u sa 、u sab 、u sc is the instantaneous value of the three-phase AC voltage of ABC, u d 、u q is the AC voltage amplitude in the dq coordinate system, and α is the A phase voltage angle.

[0019] Furthermore, in step 12:

[0020] The positive sequence voltage is:

[0021]

[0022] Among them, u qrel for u q Obtained after a quarter cycle delay.

[0023] Furthermore, the method also includes:

[0024] Step 5, adjust the frequency of the three-phase AC voltage, and perform steps 1 to 4 again.

[0025] Furthermore, the frequency of the three-phase AC voltage is adjusted as follows:

[0026] By periodically changing the sign of the adjustment angle DeltaAngle, the frequency of each phase of the three-phase AC voltage is superimposed with AngleAdd*T, where DeltaAngle is a set value that can be issued through the HMI software.

[0027] Furthermore, the three-phase AC voltage is obtained through the current inner loop control loop.

[0028] Furthermore, step 3 specifically includes:

[0029]

[0030] Among them, Angle(T) is the first Angle, and Angle(2T) is the second Angle.

[0031] An island detection system based on a high-voltage chain energy storage system comprises: an output voltage frequency detection module and an output voltage regulation module;

[0032] The output voltage regulation module is used to obtain the voltage phase angle through phase locking, calculate the grid voltage frequency Freq_Cal, and change the output voltage modulation wave by adjusting the voltage phase angle obtained through phase locking at regular intervals;

[0033] The output voltage frequency detection module is used to determine whether the energy storage system has islanding phenomenon according to the frequency fluctuation range.

[0034] Furthermore, the high-voltage chain energy storage system includes a battery module, a BMS, a PCS power link, an energy storage cabin and an energy management system. Each PCS power link includes a PCS power module, a cluster of energy storage batteries and a BMS system.

[0035] The beneficial effects of the present invention are that, compared with the prior art, the present invention has the following advantages:

[0036] The present invention can be applied to island detection of energy storage systems with similar topologies. When a grid fault occurs in the AC voltage in the figure, the control device of the high-voltage chain energy storage system can use the method of the present invention to quickly detect the AC grid fault, prevent the energy storage system from operating in an island state, ensure that the protection device of the grid system can operate correctly, and make the grid operate within the control range of the power company. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of an island detection system for a high-voltage chain energy storage system.

[0038] Figure 2 Schematic diagram of the output voltage regulation method of the high-voltage chain energy storage system.

[0039] Figure 3 This is the control principle flow chart of the phase-locked loop.

[0040] Figure 4 Schematic diagram of an island detection method for a high-voltage chain energy storage system. DETAILED DESCRIPTION

[0041] The present application is further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present application.

[0042] The high-voltage chain energy storage system includes battery modules, BMS, PCS power links, energy storage cabins and energy management systems. Each PCS power link consists of a PCS power module, a cluster of energy storage batteries and its BMS system.

[0043] The main circuit topology of the high-voltage chain energy storage system includes three groups of chain energy storage power modules, each group of chain energy storage power modules is composed of N chain energy storage power modules in series. Each chain energy storage power module includes: 1 PCS power module and 1 cluster of energy storage batteries.

[0044] The island detection method of the embodiment of the present disclosure is as follows: Figure 1 As shown, it includes: output voltage regulation module and output voltage frequency detection module. The detailed design of each functional module is described below:

[0045] The output voltage frequency detection module periodically adjusts the output voltage control signal of the high-voltage chain energy storage system, that is, the modulation wave, so that the AC port voltage of the high-voltage chain energy storage system has periodic frequency fluctuations. By detecting whether the frequency fluctuation range exceeds the island detection frequency threshold, it is determined whether the energy storage system is in an island state.

[0046] The output voltage regulation module is specifically implemented as calculating the frequency Freq_Cal of the current voltage based on the change in the output angle Angle of the phase-locked loop between two adjacent control cycles, DeltTheta (DeltThea is the difference between the values ​​of Angle in two adjacent control cycles, angle(T) and Angle(2T)) and the control cycle time T. Then, based on whether the absolute value of the difference between the current calculated frequency Freq_Cal and the reference frequency Freq_Ref exceeds the island detection frequency threshold DeltFreq, it is determined whether the system is in an island state.

[0047] The control block diagram of the high-voltage chain energy storage system is as follows: Figure 2 As shown, the phase-locked loop of the three-phase AC voltage is phase-locked to obtain the voltage phase angle Angle. The instantaneous active current reference value and the instantaneous reactive current reference value of the energy storage system are obtained by calculating the cosine value and sin value of this angle as well as the active current amplitude reference value and the reactive current amplitude reference value. Then, the modulation wave signal of the energy storage system is obtained through the current inner loop control loop, thereby controlling the port voltage of the energy storage system. The control block diagram of the phase-locked loop is shown in FIG. Figure 3 As shown, it mainly includes abc / dq coordinate transformation, positive sequence voltage extraction, and PI regulation. The abc / dq coordinate transformation is:

[0048]

[0049] In the above coordinate transformation formula, u sa 、usb 、u sc is the instantaneous value of the three-phase AC voltage of ABC, u d 、u q is the AC voltage amplitude in the dq coordinate system, and α is the A phase voltage angle.

[0050] u q After a quarter-cycle delay, we get u qrel , and finally the positive sequence voltage is:

[0051]

[0052] Will The difference is compared with 0 as the input of the PI regulation link, and the output of the PI regulation link is the voltage phase angle Angle. According to the values ​​of this angle in two adjacent control cycles Angle(T), Angle(2T) and the control cycle T, the grid voltage frequency Freq_Cal can be calculated, and the formula is as follows:

[0053]

[0054] The modulation wave calculation formula is as follows:

[0055]

[0056]

[0057]

[0058] U aref , U bref , U cref is the three-phase modulation wave, kg is the current inner loop coefficient, L is the inductance of the three-phase bridge arm of the energy storage system, I aref ,I bref ,I cref is the three-phase reference current, I a ,I b ,I c is the three-phase current of the energy storage system, U sa , U sb , U sc is the three-phase voltage of the energy storage system grid-connected point, and T is the control period of the energy storage control system.

[0059] The above modulation wave calculation formula is mainly for achieving the completeness of the description of the control system of the high-voltage chain energy storage system, and explains the method of adjusting the output voltage.

[0060] After applying the method of the present invention, Figure 2 and Figure 3As shown in the figure, after the island detection function is enabled, by periodically changing the sign of the adjustment angle DeltaAngle (this angle is a set value and can be sent down through the HMI software), the output angle of the phase-locked loop can be superimposed with a periodic fluctuation angle AngleAdd, so that the modulation wave U generated by the current inner loop aref , U bref , U cref U sa , U sb , U sc Angle changes, such as U sa The sampling voltage value is

[0061] U sa =V a *coswt

[0062] Where V a is the voltage amplitude of phase A. After adding the angle AngleAdd, it becomes

[0063] U sa =V a *cos(w*t+AngleAdd*T)

[0064] As a result, the energy storage system modulation wave U aref , U bref , U cref The frequency changes.

[0065] The specific implementation of the frequency calculation module in the method of the present invention is that the frequency Freq_Cal of the current voltage can be calculated based on the voltage phase angle Angle of the phase-locked loop, the change amount DeltTheta between two adjacent control cycles and the control cycle time T. The frequency judgment module is to judge whether it is in an island state based on whether the absolute value of the difference between the current calculated frequency Freq_Cal and the reference frequency Freq_Ref exceeds the island check frequency difference threshold value DeltFreq.

[0066] When the energy storage system is in a non-island state, the energy storage system port sampling voltage U sa , U sb , U sc Affected by the grid voltage clamping effect, even when the island detection is enabled, the calculated frequency Freq_Cal is basically the same as the frequency of the grid voltage; when the energy storage system is in an island state, the energy storage system port sampling voltages Usa, Usb, and Usc completely depend on the output voltage of the energy storage system, that is, the modulation voltage generated by the modulation wave. Therefore, by periodically adjusting the phase-locked loop output angle, the frequency change of the output voltage can be achieved, and finally the energy storage system is detected to be in an island state, realizing the island detection function of the present invention.

[0067] In summary, if Figure 4 As shown, an island detection method based on a high-voltage chain energy storage system includes the following steps:

[0068] Step 1, by phase-locking the phase-locked loop of the three-phase AC voltage of the high-voltage chain energy storage system, the voltage phase angle Angle is obtained;

[0069] Step 2, obtaining a first Angle and a second Angle according to the voltage phase angle Angle and the control period T of the energy storage control system, wherein the first Angle and the second Angle are values ​​of two adjacent control periods;

[0070] Step 3, calculating the grid voltage frequency Freq_Cal according to the first Angle and the second Angle;

[0071] Step 4: If the absolute value of the difference between Freq_Cal and the reference frequency Freq_Ref exceeds the islanding check frequency difference threshold value DeltFreq, it is determined that an islanding phenomenon occurs in the energy storage system.

[0072] The applicant of the present invention has made a detailed explanation and description of the implementation examples of the present invention in conjunction with the drawings in the specification. However, those skilled in the art should understand that the above implementation examples are only preferred implementation schemes of the present invention, and the detailed description is only to help readers better understand the spirit of the present invention, but not to limit the scope of protection of the present invention. On the contrary, any improvements or modifications based on the inventive spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. An island detection method based on a high-voltage chain energy storage system, characterized in that: The high-voltage chain energy storage system includes a battery module, a BMS, a PCS power chain link, an energy storage cabin, and an energy management system. Each PCS power chain link includes a PCS power module, a cluster of energy storage batteries, and a BMS system. The detection method includes the following steps: Step 1, by phase-locking the phase-locked loop of the three-phase AC voltage of the high-voltage chain energy storage system, the voltage phase angle Angle is obtained; Step 2, obtaining a first Angle and a second Angle according to the voltage phase angle Angle and the control period T of the energy storage control system, wherein the first Angle and the second Angle are values ​​of two adjacent control periods; Step 3, calculating the grid voltage frequency Freq_Cal according to the first Angle and the second Angle; Step 4: If the absolute value of the difference between Freq_Cal and the reference frequency Freq_Ref exceeds the islanding check frequency difference threshold value DeltFreq, it is determined that an islanding phenomenon occurs in the energy storage system; Step 5, adjusting the frequency of the three-phase AC voltage, and performing steps 1 to 4 again; The adjusting the frequency of the three-phase AC voltage includes: adjusting the sign of the angle DeltaAngle by timed changes so that the frequency of each phase of the three-phase AC voltage is superimposed with AngleAdd*T, wherein DeltaAngle is a set value.

2. The island detection method based on a high-voltage chain energy storage system according to claim 1 is characterized in that: The step 1 specifically includes: Step 11, performing phase locking through a phase-locked loop of a three-phase AC voltage and performing abc / dq coordinate transformation; Step 12, extracting the positive sequence voltage; Step 13, taking the positive sequence voltage as the input of the PI regulation link, and outputting it as the voltage phase angle.

3. The island detection method based on a high-voltage chain energy storage system according to claim 2 is characterized in that: In step 11: The abc / dq coordinate transformation is: Where u sa 、u sab 、u sc is the instantaneous value of the three-phase AC voltage of ABC, u d 、u q is the AC voltage amplitude in the dq coordinate system, and α is the A phase voltage angle.

4. The island detection method based on a high-voltage chain energy storage system according to claim 3 is characterized in that: In step 12: The positive sequence voltage is: Among them, u qrel for u q Obtained after a quarter cycle delay.

5. The island detection method based on a high-voltage chain energy storage system according to claim 1 is characterized in that: The three-phase AC voltage is obtained through the current inner loop control loop.

6. The island detection method based on a high-voltage chain energy storage system according to claim 1 is characterized in that: The step 3 specifically includes: Among them, Angle(T) is the first Angle, and Angle(2T) is the second Angle.

7. An island detection system based on a high-voltage chain energy storage system, used to execute any of the methods described in claims 1-6, characterized in that: The system comprises: an output voltage frequency detection module and an output voltage regulation module; The output voltage regulation module is used to obtain the voltage phase angle through phase locking, calculate the grid voltage frequency Freq_Cal, and change the output voltage modulation wave by adjusting the voltage phase angle obtained through phase locking at regular intervals; The output voltage frequency detection module is used to determine whether the energy storage system has islanding phenomenon according to the frequency fluctuation range.

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