Optical storage and charging hybrid micro-grid direct current area protection method

Abstract

The invention discloses an optical storage and charging hybrid micro-grid direct current area protection method. The method comprises the following steps: firstly, establishing a topological structure matrix of a protection area, and setting a pre-tripping matrix and an extended tripping matrix based on the topological structure matrix in advance; acquiring information such as voltage and current of the whole protection area in real time through the area protection center; generating a fault identification matrix of the protection area by using the fault judgment result; and calculating a tripping command matrix by using the fault identification matrix and the pre-tripping matrix, driving the circuit breaker to trip, and realizing a backup protection function. And when the circuit breaker fails, generating a failed circuit breaker matrix and calculating an extended tripping command matrix to realize circuit breaker failure protection. The method is suitable for direct-current subnet backup protection of the optical storage and charging hybrid microgrid, and all backup protection functions of the direct-current subnet are realized only by using one regional protection device.

Description

Technical Field

[0001] The present invention belongs to the field of operation, control and relay protection of a hybrid microgrid composed of photovoltaic, energy storage and charging loads, and in particular to a DC area protection method for a photovoltaic, energy storage and charging hybrid microgrid. Background Art

[0002] Under the "dual carbon" goal, renewable energy power generation will gradually occupy a dominant position in China's energy structure. In the context of large-scale distributed consumption of renewable energy, the development of an AC / DC hybrid microgrid that integrates "photovoltaic storage and charging" is an important technical route. The photovoltaic storage and charging hybrid microgrid has the characteristics of both AC microgrid and DC power grid, more efficiently integrating distributed power sources, energy storage devices and electric vehicle charging loads, and improving the operating efficiency of the energy system.

[0003] In order to ensure the safe operation of the hybrid microgrid with photovoltaic storage and charging, the relay protection system is required to be able to quickly and sensitively isolate the faulty equipment when a fault occurs. The relay protection technology of AC microgrid is mature, but for the DC subgrid in the hybrid microgrid, due to its complex fault characteristics, the relay protection method is required to have higher sensitivity and selectivity. The DC subgrid protection should be able to reflect various faults of the converter, DC line and DC bus. Existing technologies include:

[0004] (1) Converter station protection

[0005] In addition to simple and reliable overcurrent protection, converter station protection also uses main protection and backup protection based on differential principle, including pole differential protection, converter differential protection and bridge arm differential protection. However, pole differential protection can only reflect ground faults in converter stations, while converter differential protection and bridge arm differential protection may not be sensitive enough to faults on the AC outlet side of converters, and there is a risk of refusal or misoperation.

[0006] (2) DC line protection

[0007] DC line protection includes boundary protection and distance-measuring protection using single-ended measurement, and current differential principle and directional pilot protection using double-ended measurement. Among them, single-ended measurement protection cannot cover the entire length of the DC line in order to ensure selectivity. Double-ended measurement protection requires the transmission of information at both ends of the line, which has high requirements for the communication system, and the protection speed is difficult to meet the needs of rapid removal of DC faults. In addition, DC line protection is easily affected by fault transition resistance, and the protection sensitivity is not high, which can easily cause protection refusal and false operation.

[0008] (3) DC bus protection

[0009] The DC bus is mainly protected by differential protection. Although differential protection can quickly and selectively eliminate faults, it is greatly affected by transition resistance. In the case of high-resistance faults, the protection may refuse to operate. In addition to bus protection based on the differential principle, traveling wave polarity can also be used to identify bus faults. However, for DC buses with many connected lines, when a fault occurs, the traveling wave will produce complex refraction and reflection behavior, and the performance of the protection principle based on traveling wave polarity will be reduced.

[0010] In summary, the existing protection principles for single components have problems to varying degrees, such as difficulty in achieving full coverage of the protection range and insufficient protection sensitivity, especially the lack of backup protection with perfect performance. Therefore, it is urgent to improve the existing technology to solve the technical difficulties in the field of DC subnet protection of photovoltaic storage and charging hybrid microgrids. Summary of the invention

[0011] In order to overcome the above problems existing in the prior art, the present invention discloses a method for protecting the DC area of ​​a photovoltaic storage hybrid microgrid. First, according to the topological structure of the protection area, the protection area is divided into a plurality of component protection areas and a circuit breaker failure protection area; then, according to the positional relationship between each component protection area and the circuit breaker, a topological structure matrix of the protection area is established offline; at the same time, according to whether the circuit breaker should trip and whether the circuit breaker that should trip fails after a fault occurs in the component protection area, a pre-trip matrix and an extended trip matrix are generated respectively. When a fault occurs, the voltage, current and other information of the entire protection area are collected, and a fault identification matrix is ​​generated according to the fault judgment criteria. The trip command matrix is ​​calculated using the fault identification matrix and the pre-trip matrix to drive the circuit breaker to trip, thereby realizing the backup trip function of the protection area. When a circuit breaker fails, a failed circuit breaker matrix is ​​first generated, and then an extended trip command matrix is ​​calculated using the failed circuit breaker matrix and the pre-generated circuit breaker extended trip matrix to realize circuit breaker failure protection.

[0012] The specific technical solution adopted by the present invention is as follows:

[0013] A method for protecting a DC area of ​​a photovoltaic storage and charging hybrid microgrid comprises the following steps:

[0014] 1. Divide the protected area

[0015] As backup protection for the DC subnet of the hybrid photovoltaic storage and charging microgrid, the regional protection method of the present invention has two functions, namely, component backup protection function and circuit breaker failure protection function in the protection area. To achieve the above two functions, the protected DC subnet is divided into different component protection areas.

[0016] Assume that the DC subnet of the hybrid microgrid contains M power equipment components, including M1 converter stations, M2 DC busbars and M3 DC lines, and M = M1 + M2 + M3. The protected DC subnet is divided into M component protection zones, called A1 to A2. M , corresponding to M1 converter station areas, M2 DC bus areas and M3 DC line areas respectively.

[0017] The area where the protection should trip after the circuit breaker fails is set as the circuit breaker failure protection area. The circuit breaker failure protection area consists of all the component protection areas to which the failed circuit breaker belongs. For example, there are N circuit breakers in the protection area, counted as P i ,i=1,2,...,N。 When it belongs to the component protection area A j , also belongs to the component protection zone A k Circuit breaker P i When the circuit breaker fails, the protection zone of the circuit breaker failure is A. j +A k , where j=1,2,...,M, k=1,2,...,M.

[0018] 2. Establish information transmission channels

[0019] The core decision-making system of regional protection is concentrated in a regional protection center, where fault identification and tripping control commands are sent. In order to transmit the information of each protected element in the protection area to the regional protection center and receive the circuit breaker tripping command sent by the regional protection center, an intelligent electronic device (IED) is configured at each of the N circuit breakers in the protection area. The IED converts the collected analog signals such as voltage and current sampling values ​​into digital signals, and sends the signals to the regional protection center through an Ethernet communication network based on the IEC61850 standard protocol. The IED also transmits switch input signals such as circuit breaker position to the regional protection center through the communication network. After the regional protection center receives the sampling signals and switch input signals sent by the IED, it completes the subsequent steps of fault identification, protection tripping and circuit breaker failure judgment; the tripping commands and alarms generated by the regional protection center are sent to the IED through the communication network to complete all protection functions.

[0020] 3. Offline information settings

[0021] Before commissioning, the regional protection center completes the offline information setting, including establishing the topology matrix according to the protection area, generating the pre-trip matrix according to the topology matrix, and generating the extended trip matrix according to the circuit breaker failure protection function. The following details the generation process of the three offline information.

[0022] 3.1 Establishing the topological structure matrix

[0023] Before the regional protection is put into operation, the topological parameters of the protected DC subnet are set offline according to the positional relationship between the M component protection zones and the N circuit breakers in the protection zone, and the topological structure matrix D is automatically established by the regional protection center.

[0024] The specific method of establishing the matrix D is as follows. First, the N circuit breakers in the protection area are numbered P in sequence. i , i = 1, 2, ..., N, and then determine whether the current circuit breaker belongs to the component protection zone A1 to A1 in the order of the number from small to large. M , if it is true, it is recorded as 1, and if it is not true, it is recorded as 0. After each circuit breaker is judged, a row of elements of the matrix D is generated in the order of the component protection zone number from small to large until all circuit breakers are judged. Finally, the matrix D describing the topological structure of the protected DC subnet is formed.

[0025] Matrix D is an N×M matrix. The elements in matrix D are either 0 or 1. The specific meanings are:

[0026]

[0027] From the establishment method of matrix D and the meaning of the elements described in formula (1), it can be known that the N rows of matrix D represent the N circuit breakers in the protection area, and the M columns represent the M component protection areas in the protection area. If the element in the i-th row and j-th column of matrix D is 1, it means that the circuit breaker P i Belongs to component protection zone A j ; If the element in the i-th row and j-th column of matrix D is 0, it means that the circuit breaker P i Not in component protection zone A j .

[0028] 3.2 Generate pre-trip matrix

[0029] According to matrix D, set the pre-trip matrix T1. When the component protection zone A j When a fault occurs within, the regional protection center isolates the fault by driving the circuit breakers involved in the matrix T1.

[0030] Matrix T1 is also an N×M matrix. The elements of matrix T1 are either 0 or 1. The specific meanings are:

[0031]

[0032] According to the selectivity principle of relay protection, when a power equipment component fails, the circuit breaker involved in the component protection zone should be driven to trip first to minimize the scope of the fault. Therefore, the relationship between matrix D and matrix T1 is taken as T1 = D, that is, the component protection zone A jWhen a fault occurs in the drive element protection zone A j All included circuit breakers trip, completing the backup protection function.

[0033] 3.3 Generate extended trip matrix

[0034] When the circuit breaker driven by the backup protection fails, the other circuit breakers connected to the failed circuit breaker are driven to trip through the circuit breaker failure protection to isolate the fault, which is called the failure extension trip function. To complete the failure extension trip function, the extended trip matrix T2 is generated offline.

[0035] The establishment process of matrix T2 is as follows: according to the order of circuit breaker numbers, determine one by one whether to drive circuit breakers P1 to P after the current circuit breaker fails. 16 , when the circuit breaker is driven, the element at the corresponding position of the matrix is ​​recorded as 1, and when it is not driven, it is recorded as 0; each time a circuit breaker is judged, a row of elements of the matrix T2 is generated until all circuit breakers are judged. Finally, the matrix T2 is obtained.

[0036] Matrix T2 is an N×N matrix. The elements of matrix T2 are either 0 or 1. The specific meanings are:

[0037]

[0038] The N rows and N columns of matrix T2 represent the N circuit breakers in the protection area. If the circuit breaker P j Failure of circuit breaker P i If the circuit breaker P j Failure of circuit breaker P i If no tripping is required, the element in the jth row and the ith column of matrix T2 is 0.

[0039] 4. Realize the backup protection tripping function

[0040] After completing the offline information setting in step 3, the regional protection is put into operation to collect information in the protection area in real time. After detecting a fault, the fault identification matrix is ​​first generated, and then the circuit breaker trip command matrix is ​​generated to drive the circuit breaker to trip, complete the backup protection function, and achieve fault isolation.

[0041] 4.1 Fault Detection and Generation of Fault Identification Matrix

[0042] The IED installed at each circuit breaker of the DC subnet collects voltage and current data and sends the data to the regional protection center, which detects whether a fault has occurred. If a fault is detected, the fault identification logic of the protection is activated.

[0043] In the fault identification logic, existing protection methods are used to identify the faults of various components. For example, the distance measurement protection method proposed in reference [1] is used to identify the faults in the DC line protection zone, the DC bus fault component differential protection method proposed in reference [2] is used to identify the faults in the DC bus protection zone, and the bridge arm phase unit current differential protection method proposed in reference [3] is used to identify the faults in the converter station protection zone.

[0044] [1] Li Meng, Jia Ke, Bi Tianshu, et al. Distance-based protection for DC distribution networks[J]. Power System Technology, 2016, 40(3): 719-724.

[0045] [2]Hao Guo,Yiqing Liu,Mingyang Xu,et al.Fault Component DifferentialProtection of DC Bus in Flexible DC Distribution Network[C].2021 IEEE IASIndustrial and Commercial Power System Asia.China:Chengdu,18-21 July 2021:1145-1149.

[0046] [3]Di Yan,Yiqing Liu,Hao Guo,et al.Current Differential ProtectionBased on Bridge Phase Unit for Converter Station in Hybrid AC / DC Grid[C].2023IEEE 6th International Electrical and Energy Conference.China:Hefei,12-14 May2023:101-105.

[0047] In addition to the protection principles described by way of example, any protection method that can achieve component protection can be used in the fault identification logic of the present invention.

[0048] According to the fault identification results, a fault identification matrix F is generated. The matrix F is an M×1 matrix, and the elements of the matrix F are either 0 or 1, with the following meanings:

[0049]

[0050] The M elements of the matrix F correspond to M component protection zones. If the jth element is 1, it means component protection zone A jA fault occurs in the zone; if the jth element is 0, it means that the component protection zone A j No failure has occurred.

[0051] 4.2 Generate circuit breaker trip command matrix

[0052] After the matrix F is generated, the circuit breaker trip command matrix O1 is generated by multiplying the matrix F and the matrix T1:

[0053] O1=T1F=d k (5)

[0054] Matrix O1 is a 1×N matrix. The elements in matrix O1 are either 0 or 1. The specific meanings are:

[0055]

[0056] The result column vector d of formula (5) is k Contains component protection area A k The regional protection center is based on the column vector d k The information in sends a trip command to the corresponding circuit breaker. After the regional protection center issues the trip command, it continuously detects whether the circuit breaker that receives the trip command trips successfully. If all trips successfully, the fault isolation is completed and the backup protection function is realized; if there is a circuit breaker that has not tripped, go to step 5.

[0057] 5. Realize the extended tripping function of circuit breaker failure

[0058] After the regional protection center issues a circuit breaker tripping command based on the circuit breaker tripping command matrix, it detects whether the circuit breaker trips successfully. If the circuit breaker fails, a circuit breaker failure matrix is ​​generated. According to the circuit breaker failure matrix and the pre-generated circuit breaker extended tripping matrix, a circuit breaker extended tripping command matrix is ​​generated to drive the circuit breakers adjacent to the failed circuit breaker to trip, thereby completing the circuit breaker failure protection function.

[0059] 5.1 Generate circuit breaker failure matrix

[0060] The regional protection center is divided into column vectors d k After the information sends the trip command, the corresponding circuit breaker is continuously monitored to see if it has tripped. After a delay of Δt, if the circuit breaker is still in the closed state, it is determined that the circuit breaker has failed, and a failed circuit breaker matrix Y is generated. The matrix Y is a 1×N-order matrix, in which the element values ​​are 0 or 1, and the meaning of the element is:

[0061]

[0062] The N elements of matrix Y correspond to N circuit breakers. When the i-th element is 1, it means that circuit breaker P iFailure; if the i-th element is 0, it means that the circuit breaker P i No failure.

[0063] 5.2 Generate circuit breaker extended trip matrix

[0064] By multiplying the matrix Y and the matrix T2, the circuit breaker extended trip command matrix O2 is generated:

[0065] O2=T2Y=a k (8)

[0066] Matrix O2 is a 1×N matrix. The elements in matrix O2 are either 0 or 1. The specific meanings are:

[0067]

[0068] Operation result column vector a k Including circuit breaker P k The regional protection center should expand the information of the circuit breaker that trips when it fails. k The information in the circuit breaker sends the trip command to the corresponding circuit breaker to complete the circuit breaker failure extended trip function.

[0069] At this point, the regional protection completes all fault handling processes and waits for the fault to be cleared and the normal operation to resume after the fault current disappears.

[0070] The beneficial effects of the present invention include:

[0071] (1) Compared with the traditional single-ended backup protection method, the action time of the present invention is set to a fixed value Δt, which can ensure the selectivity of the backup protection without step-by-step coordination, shorten the backup protection action delay, and solve the problem of difficult coordination of the ring network backup protection.

[0072] (2) Compared with the single-end and double-end backup protection methods, the present invention utilizes the information of all power equipment components in the protection area, has high information utilization, and improves the sensitivity of the backup protection.

[0073] (3) Compared with the traditional backup protection scheme with separate configuration, the present invention only needs one regional protection device to realize the DC subnet backup protection that the traditional scheme requires multiple devices to complete, thereby improving the economic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 This is a schematic diagram of the DC regional protection architecture of the photovoltaic storage and charging hybrid microgrid;

[0075] Figure 2 This is a flow chart for implementing the DC regional protection method for a photovoltaic storage and charging hybrid microgrid. DETAILED DESCRIPTION

[0076] The specific implementation modes of the present invention are further described in detail below in conjunction with the drawings and embodiments, but they are not intended to limit the protection scope of the present invention. Any technical solutions obtained by equivalent replacement or equivalent transformation are within the protection scope of the present invention.

[0077] The topology of a typical PV-storage-charging AC-DC hybrid microgrid is as follows: Figure 1 As shown, the DC subnet includes photovoltaic power sources, AC / DC interconnected converters, DC / DC converters, energy storage batteries, DC charging piles and other DC loads. Figure 1 The protection scope of the DC subgrid regional protection includes power equipment components such as converters T1 to T4, DC lines Line1 to Line4, and DC buses Bus1 to Bus4. The regional protection logic judgment and centralized decision-making are completed by the "regional protection center". The flow chart of the DC regional protection of the photovoltaic storage and charging hybrid microgrid involved in the present invention is as follows: Figure 2 shown.

[0078] by Figure 1 Taking the event that the positive pole grounding fault occurs in the middle bus Bus1 and the circuit breaker P4 fails as an example, the implementation process of the regional protection method is explained. The specific implementation steps are as follows.

[0079] 1. Divide the protected area

[0080] exist Figure 1 The DC subnet of the hybrid photovoltaic storage and charging microgrid shown in the figure contains M1 converter stations, M2 DC busbars and M3 DC lines, where M1=4, M2=4, and M3=4. Therefore, a total of M=M1+M2+M3=12 component protection zones are divided. The specific relationship between the protected components and the zones is shown in Table 1.

[0081] Table 1 Figure 1 Component protection zone division of the DC subnetwork shown

[0082] Protected components Component symbols corresponding to electrical equipment Component protection zone number Inverter T1, T2, T3 and T4 <![CDATA[A1,A5,A8 and A 12 > DC bus Bus1, Bus2, Bus3 and Bus4 <![CDATA[A2, A4, A7 and A 10 > DC Line Line1, Line2, Line3 and Line4 <![CDATA[A3,A6,A9 and A 11 >

[0083] Figure 1 The DC subnet contains N circuit breakers, N = 16. The area where the protection should trip after the circuit breaker fails is divided into a circuit breaker failure protection zone, which is composed of all component protection zones where the failed circuit breaker is located. For example, when the bus Bus1 has an in-zone fault and the circuit breaker P4 fails, the circuit breaker failure protection zone is an area composed of A2+A3.

[0084] 2. Establish information transmission channels

[0085] exist Figure 1The DC subnet of the hybrid photovoltaic storage and charging microgrid shown has a total of 16 circuit breakers, each of which is equipped with an IED. The IED converts the collected analog signals such as voltage and current into digital signals, and sends the signals to the regional protection center through an Ethernet communication network based on the IEC61850 standard protocol. The IED also transmits switch input signals such as circuit breaker position to the regional protection center through the communication network. The regional protection center uses the sampling signals and switch input signals sent by the IED to complete the subsequent steps of fault identification, protection tripping, and circuit breaker failure judgment. The tripping commands and alarms generated by the regional protection center are sent to the IED through the communication network to complete all protection functions. The established data transmission channel is Figure 1 Indicated by a dotted line with a double-headed arrow.

[0086] 3. Offline information settings

[0087] Before commissioning, the regional protection center completes the offline information setting, including establishing the topology matrix according to the protection area, generating the pre-trip matrix according to the topology matrix, and generating the extended trip matrix according to the circuit breaker failure protection function. The following details the generation process of the three offline information.

[0088] 3.1 Establishing the topological structure matrix

[0089] Before the regional protection is put into operation, the topological parameters of the protected DC subnet are set offline, and the regional protection center automatically establishes the topological structure matrix D. Figure 1 The process of establishing the matrix D corresponding to the DC subgrid of the photovoltaic storage and charging hybrid microgrid shown is as follows.

[0090] First, the 16 circuit breakers in the protection area are numbered sequentially from P1 to P 16 Then, according to the numbering sequence, determine whether the current circuit breaker belongs to the component protection zone A1 to A 12 , if it is, the element at the corresponding position of the matrix is ​​recorded as 1, and if it is not, it is recorded as 0. After each circuit breaker is judged, a row of elements of the matrix D is generated until all circuit breakers are judged. Finally, the matrix D describing the protected DC subnet is obtained as:

[0091]

[0092] Matrix D shows the positional relationship between the 12 component protection zones and the 16 circuit breakers. Figure 1In the topology shown, circuit breaker P2 belongs to both component protection zone A1 and component protection zone A2, and no longer belongs to any other component protection zone. The second row of matrix D reflects the component protection zone where circuit breaker P2 is located, so the values ​​of the elements in the first column of the second row and the second column of the second row are 1, corresponding to component protection zone A1 and component protection zone A2 respectively; the rest of the elements in the first column of the second row are 0, corresponding to other component protection zones.

[0093] 3.2 Generate pre-trip matrix

[0094] According to the matrix D, the pre-trip matrix T1 is generated. The relationship between the matrix D and the matrix T1 is T1 = D, that is, the component protection zone A j When a fault occurs in the drive element protection zone A j The included circuit breaker is tripped.

[0095]

[0096] For example, the elements of the 2nd, 3rd and 4th rows of the 2nd column in the matrix T1 are 1, indicating that when a fault occurs in the component protection zone A2, the circuit breakers P2, P3 and P4 should trip.

[0097] 3.3 Generate extended trip matrix

[0098] In order to complete the failure extended tripping function, the extended tripping matrix T2 is generated offline. The generation process of matrix T2 is similar to that of matrix D. According to the order of circuit breaker numbers, it is determined one by one whether to drive circuit breakers P1 to P2 after the current circuit breaker fails. 16 , when the circuit breaker is driven, the element at the corresponding position of the matrix is ​​recorded as 1, and when it is not driven, it is recorded as 0. After each circuit breaker is judged, a row of elements of the matrix T2 is generated until all circuit breakers are judged. Finally, the matrix T2 is obtained:

[0099]

[0100] For example, the element in the first row and second column of the matrix T2 is 1, which means that after the circuit breaker P1 fails, the circuit breaker P2 should be driven to trip. The meanings of the remaining elements in the matrix T2 are similar.

[0101] 4. Realize the backup protection tripping function

[0102] After completing the offline information setting in step 3, the regional protection is put into operation, and the information in the protection area is collected in real time through the information transmission channel established in step 2. After detecting a fault, the fault identification matrix is ​​first generated, and then the circuit breaker trip command matrix is ​​generated to drive the circuit breaker to trip, complete the backup protection function, and realize fault isolation.

[0103] 4.1 Fault Detection and Generation of Fault Identification Matrix

[0104] The voltage and current data are collected by IEDs installed at each circuit breaker of the DC subnet, and the data is sent to the regional protection center, which detects whether a fault occurs. If a fault is detected, the fault identification logic of the protection is started. In the fault identification logic, the following three methods are used as examples: using a ranging protection method to identify whether a DC line fault has occurred, using a DC bus differential protection method based on a fault component to identify whether a DC bus fault has occurred, and using a bridge arm phase unit current differential protection method to identify whether a converter station fault has occurred. The following describes the generation process of the fault identification matrix F under this embodiment.

[0105] (1) DC line fault identification

[0106] The regional protection center obtained Figure 1 The four DC lines Line 1 to Line 4, namely the component protection zones A3, A6, A9 and A 11 The voltage U P and current I L as follows:

[0107]

[0108]

[0109] Where U PMx and U PNx Represents the voltage across Linex, I Mx and I Nx Indicates the current at both ends of Linex. x=1,2,3,4, corresponding to the 4 element protection zones A3, A6, A9 and A 11 .

[0110] According to the distance measurement DC line protection method, using U P and I L The fault distance L is calculated as:

[0111]

[0112] Where, L Mx Indicates the fault distance from the Linex side, L Nx Indicates the fault distance to the other side of Linex. x=1,2,3,4, also corresponding to the component protection zones A3, A6, A9 and A 11 .

[0113] Since the protection setting is set to L set =9.5km, and the values ​​of the elements in the matrix L are all greater than L set Therefore, the DC line element protection zones A3, A6, A9 and A11 No malfunction occurred inside.

[0114] (2) DC bus fault identification

[0115] The regional protection center first obtains Figure 1 The currents of the four DC busbars Bus1 to Bus4, i.e., the component protection zones A2, A4, A7 and A 10 The fault component current matrix ΔI of the maximum current branch of the DC bus is calculated by using the branch equivalent method. m_Bus And the equivalent fault current matrix ΔI of the remaining branches n_Bus .

[0116]

[0117]

[0118] In the formula, ΔI my and ΔI ny The maximum current branch of the same DC bus is recorded as branch m, and the equivalent branches other than branch m are recorded as branch n. Where y = 1, 2, 3, 4, corresponding to the component protection zones A2, A4, A7 and A 10 .

[0119] Using ΔI m_Bus and ΔI n_Bus Further calculation of the DC bus differential current matrix I d_Bus and braking current matrix I r_Bus .

[0120]

[0121]

[0122] In the formula, k Bus is the pre-set braking coefficient, take k Bus =0.5.

[0123] The calculation results of equations (18) and (19) show that the differential current corresponding to the component protection zone A2 is greater than the braking current, that is, 2.167 kA>0.225 kA, which meets the protection criterion. Therefore, the regional protection center determines that a fault has occurred in the component protection zone A2.

[0124] (3) Converter station fault identification

[0125] The regional protection center obtained Figure 1The currents of the branches of the four converter stations T1, T2, T3 and T4, i.e. the component protection zones A1, A5, A8 and A 12 The currents are respectively the AC side current I of the converter station expressed by formula (20) AC , the upper arm current of each phase unit expressed by formula (21) p_MMC and the lower bridge arm current of each phase unit represented by (22) n_MMC .

[0126]

[0127] In the formula, i az 、i bz and i cz They represent the A phase, B phase and C phase currents of the AC side of the converter station, respectively, where z = 1, 2, 3, 4, corresponding to the component protection zones A1, A5, A8 and A 12 .

[0128]

[0129] In the formula, I paz ,I pbz and I pcz They respectively represent the upper arm currents of the three phase units of the converter, namely phase A, phase B and phase C.

[0130]

[0131] In the formula, I naz ,I nbz and I ncz They respectively represent the lower arm currents of the three phase units of the converter, namely phase A, phase B and phase C.

[0132] Further use of matrix I AC ,I p_MMC and I n_MMC Calculate the differential current matrix I of the converter station protection d_MMC and braking current matrix I r_MMC :

[0133]

[0134]

[0135] In the formula, k MMC is the braking coefficient, take k MMC =0.5.

[0136] Since the matrix I d_MMC The elements in the matrix are all smaller than r_MMC The elements in the corresponding position in the matrix I d_MMC and matrix I r_MMCThe bridge arm phase unit current differential protection criterion is not met. Therefore, the component protection zones A1, A5, A8 and A 12 No malfunction occurred inside.

[0137] Finally, the regional protection center integrates the fault identification results of each component protection zone and generates the fault identification matrix F as follows:

[0138]

[0139] In the matrix F, the second element is 1, and the remaining elements are 0, indicating that only the component protection zone A2 has a fault among the 12 component protection zones.

[0140] 4.2 Generate circuit breaker trip command matrix

[0141] After the matrix F is generated, the circuit breaker trip command matrix O1 is generated by multiplying the matrix F and the matrix T1:

[0142]

[0143] The result of the operation is a column vector d k , where the second, third and fourth elements are 1, indicating that circuit breakers P2, P3 and P4 should trip when a fault occurs in the protection zone A2. The regional protection center is based on the column vector d k The information in sends a trip command to circuit breakers P2, P3 and P4 to complete fault isolation and realize the backup protection function.

[0144] 5. Realize the extended tripping function of circuit breaker failure

[0145] After the regional protection center issues a circuit breaker tripping command based on the circuit breaker tripping command matrix, it detects whether the circuit breaker tripping is successful. If the circuit breaker fails, a circuit breaker failure matrix is ​​generated. According to the circuit breaker failure matrix and the preset circuit breaker extended tripping matrix, a circuit breaker extended tripping command matrix is ​​generated to drive the circuit breakers adjacent to the failed circuit breaker to trip, thereby completing the circuit breaker failure protection function.

[0146] 5.1 Generate circuit breaker failure matrix

[0147] The regional protection center is divided into column vectors d k After the tripping command is sent, the circuit breakers P2, P3 and P4 are continuously monitored to see if they are tripped. After a delay of Δt=0.5s, if a circuit breaker is still in the closed state, it is determined that the circuit breaker has failed. In this embodiment, the circuit breaker P4 fails, and the failed circuit breaker matrix Y is generated as follows:

[0148]

[0149] In matrix Y, only the 4th element is 1, indicating that circuit breaker P4 has failed.

[0150] 5.2 Generate circuit breaker extended trip matrix

[0151] By multiplying the matrix Y and the matrix T2, the circuit breaker extended trip command matrix O2 is generated:

[0152]

[0153] The result of the operation is a column vector a k , where the 2nd, 3rd and 5th elements are 1, indicating that circuit breakers P2, P3 and P5 should trip when circuit breaker P4 fails.

[0154] The regional protection center is based on the column vector a k The information in the circuit breaker is used to send the trip command to the circuit breakers P2, P3 and P5, realizing the circuit breaker failure extended trip function.

[0155] At this point, the zone protection completes all fault handling processes and waits for the fault to be removed. After the fault current disappears, the normal monitoring state is restored.

[0156] The above is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for protecting DC area of ​​a photovoltaic storage and charging hybrid microgrid, characterized in that: The following steps are involved: (1) Division of protected areas The DC subnet of the photovoltaic storage and charging hybrid microgrid, which contains M1 converter stations, M2 DC busbars and M3 DC lines, is divided into M element protection zones, namely A1 to A M , where M = M1 + M2 + M3; the area where the protection should trip after the circuit breaker fails is set as the circuit breaker failure protection area, which is composed of all component protection areas to which the failed circuit breaker belongs. For example, there are N circuit breakers in the protection area, counted as P i , i=1,2,...,N, when it belongs to the component protection zone A j , also belongs to the component protection zone A k Circuit breaker P i When the circuit breaker fails, the protection zone of the circuit breaker failure is A. j +A k , where j = 1, 2, ..., M, k = 1, 2, ..., M; (2) Establishing an information transmission channel In order to transmit the information of each protected element in the protection area to the regional protection center and receive the circuit breaker tripping command sent by the regional protection center, an intelligent electronic device (IED) is configured at each circuit breaker in the protection area. The IED converts the collected analog signals such as voltage and current sampling values ​​into digital signals, and sends the signals to the regional protection center through an Ethernet communication network based on the IEC61850 standard protocol. After receiving the signals, the regional protection center identifies the fault according to the invention content of step (4) of the present invention, generates a tripping command message, starts the message sending task, and sends the tripping command to the IED through the communication network, forming a complete information channel; (3) Offline information settings Before the regional protection is put into operation, the topological parameters of the protected DC subnet are set offline according to the positional relationship between the M component protection zones and the N circuit breakers in the protection zone. The regional protection center first generates the topological structure matrix D, and then generates the pre-trip matrix T1 based on the matrix D. j When a fault occurs in the protection zone, the regional protection center isolates the protection zone A by driving the circuit breaker isolation element involved in the matrix T1. j Internal failure; In order to complete the circuit breaker failure protection, based on the principle that the circuit breaker failure protection should drive all other circuit breakers connected to the failed circuit breaker to trip, an extended trip matrix T2 is generated offline; (4) Realize the backup protection tripping function The voltage and current data are collected by IED installed at each circuit breaker of the DC subnet, and the data is sent to the regional protection center, which detects whether a fault occurs. If a fault is detected, the fault identification logic of the protection is started, and the fault of each component is identified in the fault identification logic. According to the fault identification results, the fault identification matrix F is generated; After the matrix F is generated, the circuit breaker trip command matrix O1 is generated by multiplying the matrix F and the matrix T1: Ο1=T1F=d k (1) Matrix O1 is a 1×N matrix. The elements in matrix O1 are either 0 or 1, and are determined according to the following criteria: The regional protection center is based on the column vector d k The component protection zone A included in k The circuit breaker information that should trip when a fault occurs sends a trip command to the corresponding circuit breaker to complete fault isolation and realize backup protection function; If the component protection zone A k After a fault occurs in the protection zone A k If the circuit breaker is not tripped, go to step (5); (5) Realize the extended tripping function in case of circuit breaker failure The regional protection center is divided into column vectors d k After the trip command is sent by the information in the middle, the corresponding circuit breaker is continuously monitored to see if it has tripped. After a delay of Δt, if the circuit breaker is still in the closed state, it is determined that the circuit breaker has failed, and the failed circuit breaker matrix Y is generated accordingly. By multiplying the matrix Y and the matrix T2, the circuit breaker extended trip command matrix O2 is generated: O2=T2Y=a k (3) The matrix O2 is a 1×N matrix. The elements in the matrix O2 are either 0 or 1, and are determined according to the following criteria: The regional protection center is based on the column vector a k The circuit breaker P included in k In case of failure, the circuit breaker information that should be extended and tripped should be sent to the corresponding circuit breaker to complete the circuit breaker failure extended tripping function.

2. The method for protecting DC area of ​​a photovoltaic storage and charging hybrid microgrid according to claim 1 is characterized in that: In step (3), the topology matrix D contains the position relationship information of the component protection area and the circuit breaker in the protection area: In the formula, A j is the component protection zone number, P i is the circuit breaker number, matrix D is an N×M-order matrix, the element value is 0 or 1, the N rows of matrix D represent the N circuit breakers in the protection area, and the M columns represent the M component protection areas in the protection area. If the element in the i-th row and j-th column of matrix D is 1, it means that circuit breaker P i Belongs to component protection zone A j ; If the element in the i-th row and j-th column of matrix D is 0, it means that the circuit breaker P i Not in component protection zone A j ; The specific method of establishing the matrix D is as follows: First, the N circuit breakers in the protected area are numbered P in sequence. i , i = 1, 2, ..., N, and then determine whether the current circuit breaker belongs to the component protection zone A1 to A1 in the order of the number from small to large. M , when it belongs, it is recorded as 1, and when it does not belong, it is recorded as 0; each time a circuit breaker is judged, a row of elements of the matrix D is generated in the order of the component protection zone number from small to large, until all circuit breakers are judged, and finally a topological structure matrix D describing the protected DC subnet is formed.

3. The method for protecting DC area of ​​a photovoltaic storage and charging hybrid microgrid according to claim 1 is characterized in that: In step (3), the pre-trip matrix T1 contains the tripping information of the circuit breaker when the component protection zone fails: Matrix T1 is an N×M matrix, the elements of which are either 0 or 1. The relationship between matrix D and matrix T1 is T1=D, i.e., the element protection zone A j When a fault occurs in the drive element protection zone A j The included circuit breaker trips, completing the backup protection function.

4. The method for protecting DC area of ​​a photovoltaic storage and charging hybrid microgrid according to claim 1 is characterized in that: In step (3), the extended tripping matrix T2 contains the information of the non-failed circuit breakers that should trip after a circuit breaker fails in the protection area: The matrix T2 is an N×N matrix. The elements of the matrix T2 are either 0 or 1. The N rows and N columns of the matrix T2 represent the N circuit breakers in the protection area. If the circuit breaker P j Failure of circuit breaker P i If the circuit breaker P j Failure of circuit breaker P i If no tripping is required, the element in the jth row and the ith column of matrix T2 is 0; The establishment process of matrix T2 is as follows: according to the order of circuit breaker numbers, determine one by one whether to drive circuit breakers P1 to P after the current circuit breaker fails. 16 When the circuit breaker is driven, the element at the corresponding position of the matrix is ​​recorded as 1, and when it is not driven, it is recorded as 0. Each time a circuit breaker is judged, a row of elements of the matrix T2 is generated until all circuit breakers are judged, and finally the matrix T2 is obtained.

5. The method for protecting DC area of ​​a photovoltaic storage and charging hybrid microgrid according to claim 1 is characterized in that: In step (4), the fault identification matrix F contains the fault information in each component protection zone: The matrix F is an M×1 matrix. The M elements of the matrix F correspond to M component protection zones, and the values ​​are 0 or 1. If the jth element is 1, it means that the component protection zone A j A fault occurs in the zone; if the jth element is 0, it means that the component protection zone A j An out-of-zone fault occurs or the system operates normally; In the fault identification logic, after the fault identification results are obtained by respectively using the DC line fault identification method, the DC bus fault identification method and the converter station fault identification method, the matrix F is generated.

6. The method for protecting DC area of ​​a photovoltaic storage and charging hybrid microgrid according to claim 1 is characterized in that: In step (5), the failed circuit breaker matrix Y contains the information of failed circuit breakers in the protection area: The matrix Y is a 1×N-order matrix. The N elements of the matrix Y correspond to the N circuit breakers, and the values ​​are 0 or 1. When the i-th element is 1, it means that the circuit breaker P i Failure; if the i-th element is 0, it means that the circuit breaker P i No failure.

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